GEODETIC SURVEYS IN THE UNITED STATES
THE BEGINNING AND THE NEXT ONE HUNDRED YEARS
1807 - 1940
Joseph F. Dracup
Coast and Geodetic Survey (Retired)
12934 Desert Glen Drive
Sun City West, AZ 85375-4825
ABSTRACT
The United States began geodetic surveys later than most of the world's major countries, yet itsachievements in this scientific area are immense and unequaled elsewhere. Most of the work wasdone by a single agency that began as the Survey of the Coast in 1807, identified as the CoastSurvey in 1836,renamed the Coast and Geodetic Survey in 1878 and since about 1970 theNational Geodetic Survey, presently an office in the National Ocean Service, NOAA. Anintroduction containing a brief history of geodetic surveying to 1800 is followed by accounts ofthe American experience to 1940. Broadly speaking the 1807-1940 period is divided into threesections: The Early Years 1807-1843, Laying the Foundations of the Networks 1843-1900 andBuilding the Networks 1900-1940. The scientific accomplishments, technology developments,major and other interesting events, anecdotes and the contributions made by the people of eachperiod are summarized.
PROLOGUE
Early Geodetic Surveys
And
The British-French Controversy
The first geodetic survey of note was observed in France during the latter part of the 17th andearly 18th centuries and immediately  created a major controversy. Jean Picard began an arc oftriangulation near Paris in 1669-70 and continued the work southward until his death about 1683.His work was resumed by the Cassini family in 1700 and completed to the Pyrenees on theSpanish border prior to 1718 when the northern extension to Dunkirk on the English Channel wasundertaken.
The survey created a major controversy. For the results indicated that the earth was a prolateellipsoid, which contradicted Issac Newton's 1687 postulate that it was an oblate figure. Toresolve the hue and cry that followed, the French Academy of Sciences in Paris proposed in 1733that the length of the meridian be measured near the equator and compared with that obtained inFrance. Later it was decided to do the same in the Arctic region. The Torne River valley north ofTornio in Lapland on the Swedish-Finnish border was chosen as the northern site andobservations were begun in 1736 and completed two years later.
The results showed conclusively that one degree of the****meridian was longer in Lapland than atParis and proved Newton's postulate to be correct. The expedition to Peru, the present dayEcuador departed in 1735 and returned nine years later with results that confirmed the Laplandfinding, i.e. one degree of the meridian is shorter at the equator than in France.  
Early Instrumentation
These truly remarkable efforts by the French and their associates were carried out with veryprimitive instruments in comparison with equipment available 50 years later, yet the very bestavailable then. Furthermore, the observations were secured under extreme conditions especially inthe high Andes of South America. In Peru, the angle observations were made with quadrantshaving 2-3 ft. radii and two telescopes, one fixed, the other moveable and equipped withmicrometers for finer readings, the latter used perhaps for the first time. The horizon was closedon each set of observations and usually involved 6 or 7 angles. The average closing error was onthe order of 2 minutes indicating the accuracy of each angle at 20" to 30". 
Base lines in Peru were measured using wooden rods, each 20 feet long and were standardizeddaily or more often with an iron toise (about 6.4 English feet) that was carried along and kept inthe shade. The base line in Lapland was measured over the frozen Torne River using similar,although longer (33 ft.) apparatus. 
Great Britain
Great Britain began geodetic surveys in 1784 under the direction of Major General William Roy.A site for the first base line, about 5 miles in length, was selected on Hounslow Heath in what ispresent day west London and the initial measurement was made using rods of Riga pine. Largeerrors were noted between measurements made when the rods were wet and dry and the line wasremeasured with glass tubes constructed by Jesse Ramsden. After 1791 base lines were measuredwith 100 foot steel chains. Jesse Ramsden's theodolite with a 3 ft. circle reading to 1" built in1787 was used for the angle observations and despite its weight of about 300 lbs. good progresswas obtained in the triangulation including a connection between Dover and France in 1787. Roydied in 1790 and after a delay of about one year, the triangulation was resumed and completed in1822. Between 1936-1950 a new, denser network with ties to several points of the earliertriangulation was observed.
Ramsden's Direction Theodolite
Ramsden's direction theodolite is certainly among the 4 or 5 greatest technological advances everin geodetic surveying. As a case in point, prototypes continue in use by almost all countries. In thefield of general surveying however, the invention by the French of the repeating theodolite about1790 is of equal importance for it is the basis for the instrument most surveyors have employed.Regardless of their almost universal use in the private sector, repeaters have been shown to be lessaccurate than direction instruments. In theory, the opposite is the case, in practice however,repeaters' more moveable parts and mechanical motions required to operate them contribute tolarger error sources. 
As for the French, as you might expect they still preferred repeating theodolites for higher ordersurveys as late as 1963 when a new connection between England and France was made.Instruments employed that year were repeating types, presumably reading to 1" with eye pieceshaving moveable cross hairs so that as many as 10 readings could be obtained from each pointing.One point of interest. This new connection between Portsmouth and Cherbourg was only possiblebecause Bilby towers were available.
First Level Datum
As might be anticipated The Netherlands established the first level datum in 1682 and carried outsurveys along rivers and some shoreline between 1797 and 1812. However, the first geodeticleveling was not begun until 1875. By contrast, Great Britain started their geodetic leveling in1841 and completed it about 20 years later. In almost all instances geodetic levelings wereundertaken after the triangulation was well on its way or completed.
By 1800, most of the countries of Europe had drawn up plans or were on their way in establishingtriangulations that in 1842 spanned the continent from the Mediterranean Sea on the south to theArctic regions on the north and from Ireland, England and the Atlantic Ocean on the west to theinterior of Russia on the east.
Ferdinand R. Hassler -- The Founder
The United States entered this world of geodesy in 1807 and while 25 years passed before theprimary work could be initiated, its achievements were soon recognized by much of the world. Atthe beginning and along the way for 25 years however, there were many trials and tribulations tobe overcome. The country was very fortunate indeed that a man of the caliber of Ferdinand R.Hassler was selected to lead the effort for one of lesser resolve would have given up early, theproblems were many and difficult. Hassler was 37 years old when he was named the firstsuperintendent of the Survey of the Coast and 62 when he began the first major triangulation in1832. There were many depressing and disillusioning periods for him in the intervening years.
The 1807-1940 period is divided into three sections: The Early Years 1807-1843, Laying theFoundations of the Networks 1843-1900 and Building the Networks 1900-1940. Some of thematerial such as that related to instruments and computations is given intoto in one section oranother even though the period covered spans two or more sections. Also, the brief histories forGeodetic Astronomy, Gravity and Reconnaissance Surveys cover the years 1807-1990. 
THE EARLY YEARS 1807-1843
1807: Survey of the Coast Created
Geodetic surveying began in the United States on February 10, 1807 with the creation of theSurvey of the Coast by Congress in the presidency of Thomas Jefferson. Ferdinand R. Hassler, aSwiss born geodesist, who conceived the plan was placed in charge and served in that capacity onand off until his death in 1843. Nothing was accomplished for several years because appropriatedfunds were not released due to political opposition and unsettled conditions in Europe, the sourceof needed equipment. Finally in 1811, $25,000 was disbursed and Hassler immediately went toEngland to have instruments made to his design and specifications and to purchase otherequipment and scientific books. He remained there during the War of 1812, returning in 1815. 
First Field Surveys
First field surveys were carried out in 1816-17 near New York City where a small scheme oftriangulation consisting of 11 points, scaled by two measured base lines was accomplished to anaccuracy that would approach present day second-order, class I. Hassler performed thereconnaissance to select the station sites, directed the base line measurements and observed all theangles with the recently acquired 24 in. theodolite, built by Edward Troughton of London to hisspecifications. 
The first point occupied for geodetic observations in the U.S. was identified as WEASEL locatedon a low mountain about 2 miles south of Patterson, NJ on July 16, 1817. It was marked by a 6"deep drill hole filled with sulphur. In 1934, it was reported that the top of the mountain had beenblasted off destroying the station. Blasting is among the very few ways to obliterate a mark of thistype. 
None of the original stations are thought to exist today, although WEASEL and SPRINGFIELDwere included in the primary triangulation southward from NYC observed in 1838. StationCHERRY HILL, one end of the base line at the northern end of scheme, near Englewood, NJ wasdestroyed by sub-division construction in the late 1970's only a few days before personnel werescheduled to move the point to a protected area. In 1987, the American Society of Civil Engineersplaced a plaque at the approximate location of original station CRANETOWN, north ofMontclair, NJ, noting the site as a National Historic Civil Engineering Landmark.
Hassler Dismissed
Almost immediately on its completion, politics reared its ugly head once again and Hassler wasdismissed. For about 15 years he tried his hand at several occupations before being reappointed tohis position in 1832. First he worked as an assistant on the U.S.-Canada northeast boundarysurveys, then made an unsuccessful attempt at farming in a remote site on the St. Lawrence Riverwhere his wife left him. After that he took a position as a gager at the NY Custom House,followed by a period of unemployment during which he wrote several books on advancedmathematics and developed the polyconic map projection still used today. Finally in 1830, hereceived an appointment as superintendent of the new Office of Weights and Measures. Thisoffice remained in the Coast and Geodetic Survey until 1901 when it was spun off to become theNational Bureau of Standards. This was a dark period for both Hassler and American geodesy. 
Hassler Reappointed
Once back on the job he immediately began geodetic surveys on Long Island, NY that havecontinued, more or less unabatedly until today. The instruments and equipment that Hassler hadmade or purchased were more than adequate for the task at hand. This was attested to by aFrench astronomer who said in 1832 --- at the time of construction, the instruments were twentyyears in advance of the science of Europe. Having the best of tools is no guarantee, of course forthe best of results. In surveying best means the most accurate and to reach that goal requires, inaddition to the instrumentation, trained and conscientious personnel and proper observingprocedures. The sum total of all the requirements can be broadly categorized as standards ofaccuracy. In that regard, Hassler set standards of highest accuracy for these early surveys thatremain the hallmark of American geodetic work. 
He personally made all the observations at the primary stations, yet at the same time trained hisassistants James Ferguson and Edmund Blunt on the secondary surveys so that they could step inwhen necessary to do his job --- and they did. In the  year after Hassler's death in 1843, Fergusonmeasured the KENT ISLAND base line in Maryland, Blunt the MASSACHUSETTS base, andthey shared his role in observing the primary triangulation. 
The first station occupied was BUTTERMILK on June 11, 1833. It still exists and is located onwhat is now the Rockefeller estate in Westchester County, NY. 
The Great Theodolite
Prior to October 18, 1836, the observations were made using the 24 in. theodolite mentionedpreviously. On that day and until his death in 1843, he employed a 30 in. instrument that heproudly called the Great Theodolite. Designed by himself, built by Troughton, the finestinstrument of its day was used first at station WEST HILLS on the northern shore of Long Island,a point that remains in place even now. Its weight of 300 lbs. was of little concern to Hassler,having used a 36 in. Ramsden theodolite, an instrument of similar weight in the trigonometricalsurvey of Switzerland. He simply strengthened the oversize carriage used for transporting the 24in. instrument, a fairly  heavy piece in itself weighing perhaps 200 lbs. 
Two characteristics of the Great Theodolite are seldom mentioned, one, it was designed as arepeating instrument and two, it had a 24 in. vertical circle. Hassler employed it in the directionmode as did others later, until destroyed in 1873 and it must be assumed that the finalconstruction was as a direction theodolite. 
Hassler's Base Lines
The two base lines measured for the 1816-17 survey at Gravesend Bay near present day ConeyIsland (4.7 mi) and at Englewood, NJ (5.8 mi) were not considered accurate enough nor probablylong enough to scale the primary triangulation then underway. Both bases were measured withiron chains, each link one meter in length. Accordingly, Hassler measured his only primary baseline at Fire Island on the south shore of Long Island in 1834 using four 2 meter iron bars laid endto end. It was not a direct measurement. In order to take advantage of the level beach, theprincipal measurement followed a route from WEST BASE somewhat southerly of the direct lineto a point about 255 meters west of EAST BASE. The point was connected to EAST BASE byangle and distance with the distance between the terminals obtained by computation. 
His methods were acclaimed by several scientific societies, but as always the real proofs of thepudding are the agreements with the nearest base lines as computed through the triangulation.The checks were excellent, about 1:100,000 with the MASSACHUSETTS base, EPPING base,ME and KENT ISLAND base, MD, measured in 1844, 1857 and 1844 respectively and about thesame accuracy with nearby EDMI lines observed in the 1970's. 
Hassler's base apparatus was used for the MASSACHUSETTS and KENT ISLAND bases. TheEPPING base was measured with the Bache-Wurdemann compensating equipment. The FIREISLAND base is 8¾ miles in length and marked at the terminals by red sandstone monuments 4 ft.high and about 1 ft. square with a rounded top and at intervals of 2,000 meters by stonewarecones. Records state the marks are lost, however it is unlikely that much of an effort was made tofind them, especially the intermediate ones. With today's equipment it wouldn't take a huge effortto settle the question once and for all time. 
The FIRE ISLAND base was computed through the triangulation to the line WEST HILLS -RULAND on the north side of Long Island, a line Hassler called his mountain base from whichthe triangulation east and north and to the south was extended. This triangulation eventually ranfrom Calais, ME southward to Dauphin Island near Mobile, AL then westward to New Orleans,LA a distance of 1,623 miles with the field work done between 1833 and 1898.
Massachusetts Commonwealth Survey
The Coast Survey was not the only agency establishing triangulation at the time. In 1830 theMassachusetts legislature decided to prepare maps of the commonwealth based on atrigonometric survey. Colonel James Stevens was placed in charge and began operations includingthe measurement of a 7.4 mile base line along the Connecticut River, near Northampton. 
The measurement was carried out with compensating apparatus 50 ft. in length designed by Dr.Joseph Rice. No other information is available about Joseph Rice and little is known about hisapparatus although the methodology was reported in one or two scientific journals. Nevertheless,the principle he employed was about 15 years ahead of its use in the Coast Survey, albeit his workwas known there. The first application of the compensation principle was by the Ordnance Surveyof Ireland on the Lough Foyle base in 1827. 
A theodolite on loan from the Coast Survey was used for angle observations until its recall in1834. After that time an instrument of their own design was employed. Stevens resigned in 1834and Simeon Borden, formerly an assistant took over with the bulk of the work still to be done andcompleted the survey in 1838. 
The results were not published until 1846 and the positions were given as tangent planecoordinates based on the location of the points in one of 5 zones. This was the first use of planecoordinates on a large scale in America. In 1935 it was reported that little use was made of thecoordinate system, a situation not too different from that found today.
A Series of Name Changes
Hassler began using the title Superintendent of the Coast Survey in his 1836 report to theSecretary of the Treasury, the year the bureau was transferred to that department. This usagecontinued until 1865 where that and subsequent reports to 1877 showed United States CoastSurvey. In 1878 Congress changed the name to U.S. Coast and Geodetic Survey (C&GS); in1899 the U.S. was dropped. In the 1970's, the C&GS became the National Ocean Survey (NOS),later renamed the National Ocean Service (NOS) with the geodetic functions assigned to theNational Geodetic Survey (NGS), presently an office in NOS. 
The End of the Beginning
Hassler continued observing the triangulation southward and after about 10 years only hadreached southern New Jersey involving but 24 stations. Upon completing the observations atstation BURDEN he traveled to a station site in Delaware where during a severe storm he felltrying to protect his instruments and was badly injured. He returned to his home in Philadelphiawhere he died on November 20, 1843.
Thus we reach the end of the beginning. The groundwork for laying the foundation was done. Bythe turn of the century triangulation would span the nation north to south from Maine toLouisiana, east to west from New Jersey to California, over the Great Lakes and with workunderway through the middle of the country between the Rio Grande and Canada.  
LAYING THE FOUNDATIONS OF THE NETWORKS 1843-1900 
The 1807-43 era in American geodesy was totally dominated by one person, Ferdinand R.Hassler. He was head and shoulders above all others. This was not the case for the 1843-1900years, albeit several strong willed, very competent personalities prevailed for long stretches, somefor almost the entire period, but none over shadowed all others as completely for as long a time asdid Hassler. Among the elite group were Alexander Dallas Bache, George Davidson and CharlesA. Schott.
A.D. Bache, Scientist
Alexander Dallas Bache was appointed the second superintendent of the Coast Survey inDecember 1843, being eminently well qualified for the post having a learned interest in manyscientific activities. Born in Philadelphia in 1806, the great-grandson of Benjamin Franklin, agraduate of West Point at age 19 and served 3 years in the Engineers. Prior to his appointment, hewas professor of natural history and chemistry at the University of Pennsylvania and served assuperintendent of schools in Philadelphia. Later he helped form the National Academy of Sciencesand was its first president.
Congressional Decisions
The Act of 1843, passed by Congress in April of that year, defined the functions and personnelresponsibilities of the Coast Survey that, except for a few modifications, remained in place formore than a 100 years. In fact, the enabling act of 1947 did little more than restate the bases forthe bureau that were essentially unchanged from the 1843 definitions.
One proviso in the 1843 act, unfortunately, limited the bureau's activities to the coast, and thenarrowest belt of land to support the primary triangulation. Bache accepted the restriction, andimmediately went ahead with a broad plan to divide the Atlantic and Gulf coasts into ninesections, where the ongoing work (geodetic, topographic and hydrographic) would be carried onsimultaneously and to uniform standards. Two sections were added when the Pacific coastterritories were annexed.
Congress lifted the restriction in 1871, during the superintendency of Benjamin Peirce, when itgave permission for the measurement of the Transcontinental arc. In 1878, the name was changedto U.S. Coast and Geodetic Survey to reflect the bureau's responsibilities for geodetic surveysinland.
Bache's Field Activities
Bache continued Hassler's practice of personal involvement in the field work, but didn't limit hisparticipation mostly to geodetic surveys as did his predecessor; albeit he spent considerable timein making astronomic observations and measuring base lines. In regard to the latter, he designedand William Wurdemann, then a master mechanician in the Coast Survey, constructedcompensating apparatus that was used until 1873. Seven principal base lines were measured usingthe Bache-Wurdemann equipment, the last being the ATLANTA base in Georgia. Bachepersonally directed the measurements for the first three bases at DAUPHIN ISLAND, nearMobile, AL in 1847,  BODIE ISLAND, NC in 1848, EDISTO ISLAND, SC in 1850 and thesixth at EPPING, ME in 1857. Wurdemann later resigned from the Coast Survey and formed avery successful business making astronomic and geodetic instruments for clients here and abroad.
Alexander Dallas Bache died in 1867, age 61 at Newport, RI. America had lost one of its greatestscientists, however he left a legacy of excellence for his successors to build on and most were ableto do so.
Superintendents
Bache was the last of the superintendents to participate extensively in field operations, theposition had simply become too large and the responsibilities too great for such personalinvolvements. Following Bache's death in 1867, nine civilian superintendents/directors served until1929 when the position was reserved for C&GS commissioned officers. The title was changed todirector in 1920. Several of the civilian superintendents were highly regarded scientists includingBenjamin Peirce (1867-74), Julius E. Hilgard (1881-85), Thomas C. Mendenhall (1889-94) andOtto H. Tittmann (1900-15). The last civilian, E. Lester Jones (1915-29) was a veterinary surgeonby profession with an outstanding record in public administration. 
One of Jones' first acts was to propose a commissioned officer corps because of the difficulties inemploying and retaining qualified personnel for the field work due to the frequent moves andother hardships. The proposal was accepted by the Congress and the corps came into existenceduring World War I. There was one complication. The formation of the corps forced the civilianpersonnel to accept a lesser role. In addition to the director, many of the top positions in both thefield and office are reserved for officers causing occasional differences and/or resentment to arisein the civilian group towards the corps. All in all, however the arrangement has worked fairlywell, both sides usually accepting the situation as that's the way it is. 
One of the Giants
Bache was fortunate in recruiting a number of highly qualified engineers, mathematicians andother scientific types for the Coast Survey with the title of Assistant. In due course, many becamemaster jack-of-all-trades being equally at home in the several Coast Survey activities that includedin addition to geodesy, topographic mapping, hydrography, tides and currents, magnetism andothers. Among the group was George Davidson, a native of Nottingham, England whoseexceptional talents were recognized by Bache when he was head of the Philadelphia school systemand Davidson was a student. 
Joining the Coast Survey in 1845 at age 20 he trained in geodetic surveys and astronomy underthe foremost engineers in the bureau including Bache and Robert H. Fauntleroy until 1850 whenhe was sent to California with 3 other civilian assistants. Travel between the Atlantic and Pacificcoasts was not an easy journey in 1850. Overland routes were very limited, especially in themountainous regions and west of the 98th meridian those that did exist often ran through hostileIndian territory. Once beyond rail and river boat services, travel was by foot or by horse or muleconveyances. 
Transcontinental rail service wasn't available until 1869 and it was many years before a railnetwork was developed. Stage coach service from rail heads was unreliable at best andaccommodations when available, were very primitive. Davidson and his colleagues travelled byship to the Isthmus of Darien (now Panama), then by available means to the Pacific side andanother ship to San Francisco, a trip that usually took several months. 
There was no direct mail service with Washington for many years and the field records andcomputations were sent by ship as well. Duplicate and sometimes triplicate copies were made ofall records and kept on site, even occasionally retained after their safe arrival was acknowledgedfor use in the ever expanding network. 
Davidson remained on the west coast for about 45 years, the Civil War period and a few foreignassignments excepted. During his service, the Transcontinental triangulation, a k a the 39thParallel arc was completed, primary surveys near Los Angeles and Santa Barbara Channel wereunderway and coastal triangulation was extended from Mexico to Canada. 
Davidson is not credited with the earliest triangulation on the west coast, that accomplishmentbelongs to Robert D. Cutts, one of the assistants who came west with him in 1850, although wecan be sure that he was a major participant. This small network covering San Francisco Bay wasobserved to a secondary accuracy between 1851-54, with scale provided by preliminary base lines,one at the Presidio measured in 1851 and the second, the PULGAS base near Palo Alto in 1853and oriented by astronomic azimuths.
In 1876, Davidson was placed in charge of the western section of the 39th Parallel surveys andextensions to it. In the course of that work he measured base lines at Yolo County north of SanFrancisco (YOLO base 1881), LOS ANGELES base 1889, the angulation for the base expansionsand the astronomy to orient the principal triangulation. 
Survey vs. GLO
He was a man of strong personal opinions and was an ardent advocate for the Coast Survey toassume the surveying functions of the General Land Office (GLO), the present day Bureau ofLand Management. While there was support for his proposals, it is very fortunate for bothagencies that they never materialized. The Survey had done some section work for the GLO in theFlorida Keys in the 1850's and the experience was not a happy one for either side. 
There is no doubt that had his plan been accepted the section corners would have been located, atthe very least, to a minimum geodetic accuracy thus creating a cohesive network supplemental tothe national framework.  However, the cost would have been enormous and  Survey fieldpersonnel would assuredly have been bogged down executing time consuming short line surveys,often over rough terrain. 
Sooner or later Congress would have viewed this as an endless project, and it very well mighthave been just that. GLO practices were right for the time, with means now available for a totalupgrading of the system once all the legal ramifications for such an undertaking are settled. 
Although this cause was lost, most others were successful. His ability to convince James Lick tofinance the great astronomical observatory atop Mt. Hamilton is a good example of his successes. George Davidson was unquestionably the greatest field geodesist the Survey produced in the 19thcentury, the giant among giants for only men of that breed could have executed the triangulationthrough the mountain west of the time. In 1895 during William W. Duffield's superintendency(1894-97), Davidson in his 50th year of service was summarily dismissed, as were many otherexperienced employees. In his usual pragmatic fashion, Davidson accepted a professorship at theUniversity of California and went on with his life doing things his way until his death in 1911.         
Multi-Talented Schott
In the field of computations, Charles A. Schott stood alone during this period, much as GeorgeDavidson did in his area of expertise. Schott was born in Mannheim, Baden, Germany in 1826, agraduate of the University of Karlsruhe and joined the Coast Survey in 1848. Appointed chief ofthe computing division in 1856, he held the post until his resignation on December 31, 1899, after52 years of service. 
A world recognized expert on the earth's magnetic field, personally carrying out numerous fieldsurveys in the eastern U.S. and instrumental in establishing magnetic observatories at Madison,WI and Los Angeles, CA. He had a life long interest in field activities that was culminated withthe development of a contact compensating base line measuring apparatus of unique design in1881 that bears his name and was used in the same year to measure the YOLO base in California. 
As chief of the computing division he was responsible for a myriad of calculations and as was hisway took a distinct interest in all of them. Much of his efforts was directed to geodeticcomputations, especially the adjustment of the observations and investigations of the results. Onesuch examination carried out in 1878-79 relative to geodetic and astronomic data on the EasternOblique arc provided information for establishing the first national datum and conclusivelyshowed that the Clarke spheroid of 1866 fit the U.S. better than the Bessel spheroid of 1841 thenin use. 
Both results were adopted, the New England datum of 1879 as it was named is the basis for allsubsequent datums until 1983. The Clarke spheroid of 1866 still provides the best fit for thecontinental  U.S., albeit the Geodetic Reference System of 1980 (GRS 80) was adopted in 1983for other reasons. 
Schott was a prodigious writer authoring more than 160 scientific articles, papers and reportsincluding two volumes detailing the results of the primary triangulation that were hailed bygeodetic circles worldwide. The volumes are The Transcontinental Triangulation and theAmerican Arc of Parallel Sp.Pub.no.4 1900, 871pp. and The Eastern Oblique Arc of the UnitedStates and the Osculating Spheroid Sp.Pub.no.7 1902, 394pp. Charles A. Schott died in 1902. Wewill never see his kind again. 
Quadrilaterals and Central Points
Early in Bache's tenure a decision was reached for the triangulation that only quadrilaterals withboth diagonals observed, commonly called braced quadrilaterals or central point configurationswould be permitted. The reason for this specification is these figures provide at least onegeometric condition involving the angles, known as side conditions or equations.  These equationsutilize the sines of selected angles taken in a particular sequence and give a better evaluation ofthe worth of the angles than an examination of the triangle closures alone. 
This requirement was met for all the principal triangulation and most of the secondary workexcept for parts of Hassler's early net and pieces of the U.S. Lake Survey triangulation observedlater in the century.
Longitude by Wire
The first of several significant advances in American geodetic surveying that were to be made inthe next 100 years was the development by Sears C. Walker in 1847 of a method for determiningtime differences between places using the electric telegraph, invented only a year earlier. As aresult more accurate astronomic longitudes were determined leading to subsequent improvementsin Laplace corrections to astronomic azimuths. 
Once the transatlantic cables were in place later in the century the same principle was employed todetermine a more accurate cardinal longitude for North America, relative to Greenwich, than hadbeen obtained from 1065 chronometer exchanges during a previous time. This method was useduntil the 1920's before being replaced by radio signals.
Advances in Theodolites
Hassler's original theodolite was built by Edward Troughton of London during the period1811-14, had a 24 in. circle, weighted more than 150 lbs. and required a special oversize carriageto transport it. In 1836 his Great Theodolite with a 30 in. circle, also constructed by Troughtonarrived in the U.S. and was put to immediate use in the primary triangulation then being extendedeast and south of New York City. 
In the early period, segments of the primary triangulation were observed with 10 and 12 in.repeating theodolites and acceptable results were obtained. The results notwithstanding, repeaterswere rarely employed on primary work after this time. 
In due course, several lighter, more accurate instruments were designed and/or built in thebureau's instrument division. The most notable being two 20 in. circle models in 1873 made byWilliam Wurdemann, formerly of the Coast Survey and three improved versions of these modelsconstructed in 1876-77 at his shops in Dresden, Germany. 
The instruments were followed in the continuing evolution of smaller and equally accurate circlesat 25-30 year intervals by the 12 in. circle - 3 micrometer theodolite constructed by the then chiefof the division, Ernst G. Fischer about 1894 and the 9 in. circle - 2 micrometer theodolitedesigned by Douglas H. Parkhurst, head of the division in 1927. 
All direction theodolites prior to the Parkhursts were read via 3 micrometers. In the early 1950'sthe Wild T-3 theodolite, with a 5½ in. glass circle read by an auxiliary telescope, replaced the 2micrometer Parkhurst and was employed until the mid 1980's, becoming obsolete with theintroduction of the Global Positioning System (GPS). 
During the more than of 150 years of U.S. triangulation observations, diameters of horizontalcircles ranged from 30 inches in the 1830's to 5½ inches in the 1980's. Despite the huge disparitiesin weight, construction and diameter of theodolite circles, the common denominator is theaccuracy of the observed angles remain the same. 
Instruments of the time were built to last. Hassler's 30 in. theodolite, for example was in constantuse for about 37 years before being destroyed by a tornado. Its destruction is described inSp.Pub.no.7, p.47 as follows: ..... was in continuous use till November, 1873, when it met with anaccident at station SAWNEE, in Georgia. It was struck by a tornado and, not withstanding itsweight of 300 pounds, was hurled from its stand and irreparably damaged.  
 Few theodolites before the Parkhursts had vertical circles attached. Vertical angles wereobserved using separate instruments with circles only slightly smaller than the horizontal ones.
Field Specifications
Prior to 1905 no published specifications existed for making horizontal observations, although theprocedures adopted by the superintendent of the Survey in that year were those long in use. Thelack of stated requirements was not of great concern since only 4 or 5 observing units were in thefield on any given day and the observers, a very select group, were field trained, college- educatedengineers. 
This was not always the case in later periods. Between 1935 and 1970, for example, about 10times that number of units often were working on a single night. 
From the beginning, direction instruments were mostly employed in a pattern of taking direct andreverse measures on each point in turn seen by the station occupied, the sum total constituting aset. Several sets were observed with each set beginning on a different part of the circle. Thismethod of observing is attributed to Bessel, albeit it was likely used in some form prior to hisproposal. 
Eventually sets became known as positions and the initial settings for each position were assignedspecific locations on the theodolite circle. Sixteen positions evolved finally as a completeobservation for the principal triangulation with a 4" rejection limit from the mean. 
The Coast Survey rarely deviated from the general practice described above, but the Lake Surveydid on occasion by employing the method of independent angles reasoning it would reduce theeffects of tower twist, a rationale dismissed by some. 
Coast Survey observers were trained to take their measures as rapidly as possible, without forcingany of the motions or miss 'em quick in the parlance. 
Little information is readily available about the time required to complete observations in earlierperiods and it really doesn't matter much because most occupations took a week or more and afew several months. Gardens were even planted at times. Estimates to complete the 32 pointingson each signal light when using the 12 in.- 3 micrometer theodolite was 15-20 minutes. 
Once Parkhursts came into use the time was reduced by about one-third and some observersbecame very fast, with runs of 6-8 minutes per light and less recorded. Similar times were the rulewith T-3's.  
Most theodolites used by the C&GS prior to about 1950 required two observers for the mostexpeditious operation, one to point the instrument and read one of the micrometers and thesecond to read the other micrometer(s). 
Personnel assigned to observing units as recorders had to have superior arithmetic skills so as tobe able to instantly mean the 6 readings of seconds for 3 micrometer instruments and 4 readingsfor Parkhursts. Then continuing the process by reducing the readings to the initial station for eachposition and placing them on an abstract for inspection by the observer on completing his work.T-3's involved a slightly different process, the effort required was about the same as for theParkhurst.
Signals: Cones, Helios, and Lights
In Hassler's time, observations were generally taken on earthenware cone targets mounted atoppole signals. Polished metal cones for reflecting sunlight, mounted in the same fashion, continuedto be used for several decades at unmanned stations. 
By the 1840's, heliotropes came into use continuing until 1902 when they were replaced byacetylene lamps, which in turn were replaced by automobile headlights in 1916. It was longknown that daytime observations caused the triangulation to sway, probably due to unequalheating of the theodolite, despite precautions taken against it and several attempts were made inthe 1880's to observe at night, even to using a selenotrope to reflect moonlight; none proved toosuccessful. 
Selenotropes required much larger mirrors than heliotropes' 2-4 inch diameter reflectors: i.e. 6 by6 inch mirrors for 22 mile lines, 6 by 8 inch for 48 miles, 8 by 10 inch for 70 miles and lines longerthan these were not uncommon in the triangulation of the time. The sway, of course could becontrolled by inserting additional Laplace stations. After 1902 all primary observations were madeat night.
On the Mark
Accurate plumbing of theodolites and targets over station marks is requisite in making geodeticsurveys. Exact centering was always desired, however miscenterings of 0.1 to 0.2-in. and perhapsmore when high towers were involved would not be unrealistic, nor cause large errors. i.e. Amiscentering of 0.1-in. translate into a maximum error of 003 in an angle over 10 mile lines andfor a 1-in. displacement, over the same length lines the largest error would be 03. Where tripodheight stands and short towers were employed, the centering was usually done with plumb bobs. 
Prior to about 1900, when optical plummets, known as vertical collimators, came into use, highsignals were plumbed with a theodolite, from observations at two locations, 90 or 180 apart. Theearly collimators were designed for use from the top, down. Once Bilby towers replaced woodensignals, the ease in which the tripod head and light plate could be adjusted made it more practicalto plumb from the station mark, upward, and the collimators were modified accordingly. Manytheodolites introduced after 1950 had built in optical plummets, further simplifying the task.   
Base Line Measuring Apparatus
A variety of base line measuring apparatus, usually rods or bars 2-6 meters in length, encased intubes were developed, many ingeniously designed to resolve the problem of thermal expansionthrough compensating principles. The last of these apparatus and the most accurate, a duplex barset was designed by Assistant William Eimbeck in 1897 and used by him to measure the SALTLAKE base in 1897. The equipment was employed as a field standard replacing the iced barapparatus used previously for the standard kilometer section during the measurement of 9 baseson the 98th Meridian arc by Assistant Albert L. Baldwin with steel tapes in 1900. Eimbeck was along time associate of George Davidson and one of those elite mountain men mentionedpreviously. 
The first bases measured with steel tapes were the HOLTON base, IN and the ST ALBANS base,WV by Assistants Alonzo T. Mosman and R. Simpson Woodward in 1891 and 1892 respectively.Measurements were made mostly at night utilizing 4 tapes, two 50 meters in length and two 100meters in length. A 100 meter field comparator and a one kilometer section of each base weremeasured using iced bar apparatus designed by Woodward when he was associated with theUSLS. The apparatus consisted of a 5 meter steel bar immersed in melting ice in a Y shapedtrough mounted on two 3 wheel vehicles that were moved along a portable track. 
While highly accurate, it was a cumbersome device requiring about one hour to measure 100meters. Similar equipment was long used by the Bureau of Standards to standardize tapes. NoC&GS base line was completely measured with the apparatus. The 9 bases on the 98th Meridianarc were measured accordingly, except only the 100 meter comparators were established by icedbar measures, with Eimbeck's duplex bars serving as the field standard, as mentioned earlier.  
The Impact of Invar
The thermal expansion problem was finally resolved with the discovery of invar, an alloy of nickeland steel having a very low coefficient of expansion by Charles E. Guillaume, a French scientistabout the turn of the century. Tapes and wires became feasible for measuring distances. 
Following the measurement of 6 primary base lines by Owen B. French in 1906, all bases weremeasured using tapes made of invar, 50 meters in length, a much more efficient and faster methodthan those previously employed and certainly as accurate. Base line tapes were kept in sets of 4,three for the measurements and one as a comparator, all standardized prior to and after use. 
Prior to 1870, all primary base lines resulted from a single measurement with segmentsoccasionally remeasured for verification purposes. Due to the singular nature of the observations,the validity of the measurements was primarily ascertained by knowledge of the equipment andprocedures employed. Accuracy estimates were based on comparisons of the apparatus madeprior to and at the completion of the work with the field standard and by duly considered errorestimates for the various observations and actions  involved. 
In 1872-73, the ATLANTA base on Peach Tree Ridge was completely measured three times,forward in the fall, backward in the winter and forward again the following summer. Few baselines were ever completely measured twice prior to this time and to do so on 3 occasions wasprobably a geodetic first. Later, at least two complete measurements were made and when usinginvar tapes two of the measures were always made in opposite directions with the same person atthe front contact or marking end of the tape to cancel the parallax effect. 
Measuring base lines was a time consuming chore prior to tapes being employed. Sites often hadto be graded to meet the 5% slope restriction and taking observations at 6-8 meter intervals madefor slow progress, which averaged less than 0.5 mile per day for Hassler's equipment and slightlymore than one mile with compensating apparatus. Once tapes were introduced, the gradeallowance was increased to 10% and the much longer tapes made 5 miles and more progress perday routine. 
Base line apparatus followed an evolutionary path similar to that taken by theodolites, with onedistinct exception. Each new apparatus provided an improved accuracy, while there is nosignificant difference in the angles measured with the 3 footers in 1790 and those observed by thehalf footers after 1950. For example: The 3 base lines measured with Hassler's equipment had anaverage standard error (one sigma) of 1:200,000; compensating apparatus 1:310,000 and invartapes 1:675,000 or better. 
Geodetic Astronomy
Only a limited amount of Geodetic Astronomy was accomplished during the Hassler period with afew latitudes, azimuths, differences of longitude by the chronometer method and at least onelongitude being observed. However, it was not until 1847 following Sears C. Walker'sdevelopment of the telegraphic method for determining differences of longitude that all thequantities were of equal accuracy. 
Astronomic latitudes were observed using the Horrebow-Talcott method following its adoption in1851 to the present. Bache introduced the method in 1846 and the first complete set ofobservations was obtained by Assistant T.J. Lee at Thompson, MA in the same year. In the1970's, in response to contentions that the Sterneck method was more accurate, observations atmore than 30 stations showed that both procedures gave essentially the same results. 
From 1847-1922 longitudes were determined by the telegraphic method whenever possible. Afterthat time radio signals were employed. 
Azimuths were observed by a variety of procedures, although the direction method was, by far,used the most often for primary determinations. In the direction method, observations on Polarisor whatever star was used, were taken as if it is simply another signal, following the samemeasuring sequence as for triangulation. A chronometer was set for estimated local time and thetimes of measurement were corrected later for the difference with true local time determined fromobservations on time stars or radio signals, obtained prior to and immediately following theazimuth observations. About 1975, digital clocks were adapted to receive the standard radiosignal directly. Repeating theodolites were occasionally used for azimuth observations followingthe same patterns as used for angulation. 
Broken Telescopes Introduced
Latitude and longitude observations were made from 1847-88 with large transit instruments madeby Troughton and Simms of London that could be used as both meridian and zenith telescopes.Slightly smaller similar transits built by the C&GS Instrument Division were employed after thattime until 1914, when Bamberg broken telescopes were introduced. About 1960 the Wild T-4,another broken telescope instrument, replaced the Bambergs and in the 1970's the KernDKM-3A, a true universal theodolite was introduced. Astronomic azimuths were generallyobserved using regular theodolites except in the higher latitudes where any of the three astroinstruments employed after 1914 could be substituted.  Determining differences of longituderemained a problem for many years after 1847 because the telegraph lines required were notalways available, especially in the western part of the country and Alaska, and the chronometricmethod continued to be used. As a matter of fact, most of the longitude bases for the several localdatums in Alaska resulted from chronometric observations. On the other hand, telegraph lineswere sometimes extended to places specifically to determine astronomic longitudes. One suchcase was at Lake Tahoe in 1893, as part of the delineation of the  California-Nevada boundary,where it was necessary to string telegraph lines about 5 miles airline, all uphill from Genoa, NV. 
Early on, astronomic latitudes and azimuths, because of the simpler nature of the observations,were obtained more frequently. The primary reason for the observations was to obtain deflectionsof the vertical at the points by taking the difference between the observed and geodetic azimuthsand backing out the Laplace equation to compute the equivalent difference in longitude. When theastronomic longitude also is observed, the point is identified as a Laplace station althoughtechnically only the longitude and azimuth is required. 
In due course, Laplace stations were regularly spaced throughout the country. The U.S. networkwas one of the few anywhere whose orientation was rigorously controlled by Laplace azimuths atprescribed intervals. This policy began about 1910 for the work still in progress and continued inthe establishments of the North American datums of 1927 and 1983 (NAD27 and NAD83). 
The end results of the method described above for obtaining deflections of the vertical weregenerally for analysis purposes only. However, there was at least one prominent instanceotherwise where the method was employed to obtain such information needed to reduce thePASADENA base to the mountain line Michelson used in his experiments on the speed of light in1922-23. 
Astro-Geodetic Deflections 
Astronomic azimuths as observed also were used to control the first-order taped traversesobserved during the 1917-27 period. It was recognized that the Laplace corrections would bevery small in that part of the country where the traverses were measured and that the observedangles could easily absorb the differences. In 1956 a program was initiated to determineastro-geodetic deflections along the 35th parallel at about 30km.(18mi) intervals as part of aninternational study on the shape of the earth. Most of the observations were completed, somemade as part of the Transcontinental Traverse (TCT) project where more than 1,300 astronomicpositions and azimuths were measured between 1961-76. 
In 1974, a plan was drawn up to upgrade the network for NAD83 that included the measurementof several hundred new base lines, astronomic azimuths and required positions plus astronomicpositions for about 100 points, mostly base line stations where steep-slope lines (in excess of 5)were involved. The purpose of the latter was to determine deflections of the vertical for use incorrecting the observed angles. A maximum correction of 5" was found in the TETON basetriangulation, Grand Tetons, WY, an amount certainly among the largest discovered to date. 
Until 1960 almost all geodetic astronomy was accomplished by the C&GS. About that time, theDefense Mapping Agency (DMA) as part of the missile and satellite programs began observingastronomic positions at sites of particular interest to them. Later, DMA measured several legs ofthe TCT including the required astronomic positions and azimuths. Once the Global PositioningSystem (GPS) became operational in the mid 1980's, geodetic astronomy along with the classicalmethods for determining geodetic positions was obsolete. Little or no astronomic work has beendone since 1985.  
Towers, ... First of Wood
Classical triangulation was developed utilizing the higher elevations for station sites, for theobvious reasons. Whenever possible to do so, sturdy triangular-shaped wooden stands, about 4 ft.high, plumbed over the point, generally with a platform for the observer, were used to hold thetheodolite. On a few occasions in the 19th century and after about 1965, similar stands of metalwere sometimes employed. 
While ground setups were ideal, it was nevertheless not unusual to elevate the instruments furtherin order to clear various obstructions, to extend the lines of sight, to minimize refractionconditions and similar, and this was done even in the earliest time, despite the heavy weight of thetheodolites. As an example: The scaffolding and tripod at both ends of the EPPING base, ME in1857 rose 43 ft. above the surface marks, and the pole signals extended 10 ft. higher. For almost100 years, the structures were made of wood, in a few cases, the actual tree itself was used and invery rare instances, of masonry construction. Whenever possible, the stands holding the personnelwere separate from the instrument tripods. 
The sparsely settled, wide-open spaces of 19th century and early 20th century America didn't lenditself to the European practice of utilizing church spires and other high structures for triangulationstation sites. Even when available very few of these buildings were ever selected for primarystation locations because of stability problems and the need, in many instances for eccentricsetups. As a result the tall wooden towers or signals, as they were also called, required toovercome various obstacles were often engineering and architectural gems. In some cases,especially in the high plains where earth curvature was the only obstacle, shorter double towerswere topped with slender, and sometime equally as tall superstructures from which heliotropes,lights or pole targets were displayed. 
Then of Steel
The era of tall wooden towers ended in 1926 when Jasper S. Bilby, then Chief Signalman C&GS,drawing on steel windmill technology used throughout the west, erector set toys, gas pipe towersbuilt earlier by the U.S. Lake Survey and his own long experience in constructing wooden signals,designed a double tower survey signal built almost entirely of reusable steel bars and rods, heldtogether with bolts. These especially strong structures could be erected in standard configurationsto heights from 37 to 116 feet in 13 foot increments by a 5 man crew in a day or less anddismantled by a 4 man team in about half that time.
The occasional need to extend the height of in-place towers and for additional height on thehighest signals available was resolved very early with one piece sections, each 10 ft. in height, thatwere bolted to the tops of towers. As many as 3 sections, while rare, have been added to a singletower. A few bases for 129 ft. towers were later available, but seldom employed because of themuch larger area required to anchor them.  
Bilby tower components could be reused on numerous, even hundreds of times and the towerswere employed worldwide. Their first use was in 1927 in southern Minnesota where during theworking season that included other projects in the state, 96 towers were erected. As a point ofinterest, the tallest built was 156 feet (about the height of a 15 story building) on the MississippiRiver arc in 1929. 
One of a Kind
Jasper S. Bilby joined the C&GS in the 1880's as a young man, fresh off an Indiana farm andimmediately showed an uncanny ability to locate trees obstructing lines of sight, an importantattribute in a time when it wasn't easy to move about. He became skilled in signal building andreconnaissance (planning surveys), and in fact, wrote the original manual on the subjects, amongseveral special publications he either authored or co-authored. He rose through the ranks to Chiefof Party and at the time of his retirement in the 1930's, he was Chief Signalman, the highestcivilian position ever in the C&GS field service.
Station Monuments
Lasting station monuments, for obvious reasons, were always of fundamental importance ingeodetic surveys. Where rock ledges or large boulders were available, Hassler utilized drill holesfilled with sulphur or some other substance to reduce the effects of freezing. Elsewhere, buriedtruncated earthenware cones were the rule. The center of the smaller radius end marking the exactstation. Sub-surface (underground) marks also were usually set in the same fashion. In most cases,at least one reference (witness) mark was established, drill holes and cross cuts in rock structuresand truncated earthenware cones, smaller than the station marks were standard. Hassler buried thereference cones in a specific pattern, providing visible reference information to locate the generalstation site, and in addition buried small pieces of rubble, sea shells and the like found at the site,atop the station mark to aid in the recovery. 
Reference marks serve several purposes: To aid in locating the station, to verify its position, toreset the monument and for use as substitute stations. 
Versatile Concrete
Base line stations were usually marked by heavy stone posts until about 1900 when pouredconcrete monuments replaced them. From about 1850 to the turn of the century, stone posts(marble, sandstone and limestone) 2-3 ft. in length, and for sub-surface marks the same type ofposts, bottles, earthenware jugs and crocks and similar, generally replaced cones for markingstations. However, in some instances, bolts and nails cemented in drill holes, simple drill holes,cross cuts and in fact, almost any conceivable mark, in any combination with these stationmarkings were utilized. When necessary to bury the marks, a ditch 4-8 ft. in diameter and 8-18 in.deep, surrounding the station location was usually dug and filled with coal or charcoal. Onceconcrete became readily available, 2-3 ft. long tile and tin pipes filled with the substance, set overunderground marks were often employed with centers marked by bolts, nails, punch holes, etc. 
About 1900, cast bronze disks were introduced and shortly thereafter poured concretemonuments 3-5 ft. deep with sub-surface marks became the standard, where rock ledges andboulders were not available. Monuments of this type continued to be used until the mid 1980's. 
About 1965, steel rods driven to refusal with disks attached later were set for many surveys and infact, are the basis for what are believed to be the most stable marks by today's standards. 
In the 1920's, two reference marks were specified for each station and beginning in 1927, a thirdreference mark was set about ¼ mile distant for use in providing azimuth control for local surveysand for determining magnetic declination. Standard azimuth mark disks replaced azimuthreference marks about 1935. 
Bench mark monuments were of similar design until the late 1970's when special steel rod typemarks were introduced. In the 1930's, precast concrete posts with bench mark disks attachedwere used for several years. 
Prior to the late 1970's, all concrete monuments and disks were constructed of non-magneticmaterials.  Once GPS became operational, sub-surface, reference and azimuth marks were seldomset and rod type station marks predominate.  
Field Communications
Communications between observing units and on station personnel were kept simple and brief. Inthe earliest days none were usually necessary because the pole-target signals were seldomattended and when they were, a few flashes with a mirror for identification purposes and toindicate the observations were to begin and something similar on their conclusion would generallysuffice. That practice continued when heliotropes came into use during the 1840's and moststations were manned, until about 1900 when Morse code was introduced. Only a few observingunits were active in this period and the need to signal more detailed information was rare. 
John F. Hayford during his service with U.S.-Mexican Boundary Commission in the 1890'sresolved such a need for in field communications by utilizing Morse code. Once lights replacedheliotropes at the turn of the century, most observations were made at night and there were morereasons for the observers to have direct contact with the lightkeepers. For one, identification, alsolights often had to be dimmed or brightened, messages relayed in emergencies and the like. In1902 International Morse code was adopted as the vehicle to obtain that end. 
Beginning in the 1930's multiple observing parties became the rule and angle information wasoften transmitted to the Chief Observer (1st O) so that triangle closures could be computed andany required reobservations made while still on station. 
Radios were tried early in the World War II period and caused enough problems to delay theirgeneral use for about 15 years, the major one being the conversations were picked up by nearbyreceivers. In one case, locals hearing the jargon, compounded by flashing lights thought foreignagents were in the area and reported the incidents to police, who went looking for spies and foundinstead, surveyors atop towers. And, as might be expected, there were a few complaints aboutprofanity. 
By about 1960 radio technology was improved and all units were so equipped. Another eraended. No longer would lightkeepers peer off into the darkness awaiting a light blinking Dash -Dot - Dot pause Dash - Dash - Dot or DG, translated, Done here, Go to next station. 
More Territory ... More Work
Progress was slow on the principal triangulation during a few periods in the 19th century whenterritorial acquisitions, especially those with long coastlines such as Florida, Texas, the PacificCoast and Alaska created a need for immediate hydrographic surveys and other required chartinginformation. And, the Coast Survey was a small bureau, personnel-wise. 
A continuing problem, political opposition to geodetic surveys never really disappeared, althoughnot as viciously as in the Hassler years. One congressman loudly proclaimed when the C&GS wasauthorized to carry the work to the interior that it was proliferating worthless triangulationthroughout the country, and he probably had some supporters. 
The Civil War caused the longest delay as many employees went off to join the military, north andsouth. In 1863 when it appeared the thrust of Lee's Army of Northern Virginia was aimed atPhiladelphia, Bache and Davidson were sent there to aid in planning a defense for the city.Fortunately, Gettysburg ended that threat. The Spanish-American War brought more coastalterritories, the Philippine Islands and Puerto Rico among them and about the same time, theHawaiian Islands joined the U.S., all adding to the work of the bureau. 
Continent-Wide Arcs
By the turn of the century the Eastern Oblique and the 39th Parallel arcs and extensions northfrom central Kansas to Nebraska and south from San Francisco to Santa Barbara were completed.The 39th Parallel triangulation is 2,750 miles in length, probably the longest arc executed by asingle government and connects the lighthouses at Cape May, NJ and Point Arena, CA linking theAtlantic and Pacific Oceans, symbolically as well as scientifically. During the period primarytriangulation was observed in much of New England and in 1876 Assistant Charles O. Boutellemeasured an arc over the Mohawk Valley connecting this work with the Lake Survey stationsnear Buffalo. 
West of central Colorado the 39th Parallel triangulation consists of massive figures, manycontaining lines 100 miles and more in length, the longest being 183 miles betweenUNCOMPAHGRE PEAK near Ouray in Colorado and MOUNT ELLEN near Hanksville,inUtah. In the 950 mile stretch from Colorado Springs, CO to San Francisco, CA less than 40stations were required with many of the observations made by Assistant William Eimbeckbetween 1876-96. 
Great Hexagon and Davidson's Quadrilaterals
West of Salt Lake City is the Great Hexagon with WHEELER PEAK at its center connecting thestations on the Wasatch Mountains to the east with those about 200 miles to the west in Nevada.Due to the remoteness of the area and short working season it took 10 years to complete theobservations at the 7 stations involved. 
In the 1880's and 90's the only mode of travel to the station sites in the mountain west was byhorse, more likely mule, and wagon. Actually, horse and mule drawn wagons were the only meansof transportation to most station locations everywhere until motor trucks were introduced in1913. The first was a White Motor Co. 1½ ton truck, with a 30 HP engine and 25 MPH topspeed used by an astronomic party on the 104th Meridian arc. Instruments, equipment andsupplies were heavy and wherever it could be done, roads were built up the mountain as far aspossible. The one at WHEELER PEAK remains today. 
Further west the triangulation is carried over the Sierra Nevada near Lake Tahoe by very largefigures known as Davidson's Quadrilaterals with sides ranging from 57 to 142 miles in length.
Longest Line Observed
In 1878 Carlisle P. Patterson superintendent of the newly named Coast and Geodetic Survey gaveGeorge Davidson authorization to establish a station on Mount Shasta, a huge mountain innorthern California with an elevation of 14,162 ft. The real purpose for the project being tomeasure the side MT SHASTA to MT HELENA which at about 192 miles would make it thelongest triangulation line ever observed. The line MT LOLA to MT HELENA one of the sides ofDavidson's Quadrilaterals, 133 miles in length was selected as the base for the triangle. 
Assistant Benjamin A. Colonna was chosen to make the observations at MT SHASTA andGeorge Davidson at MT LOLA. Observations were not secured at MT HELENA, onlyheliotropes were shown. Colonna's description that follows of the day he was successful tells thewhole story. 
The complete article, Nine Days on the Summit of Mt.Shasta appears in The Journal -Coast andGeodetic Survey, June 1953 Number 5, pp. 145-152. Friday August 1, (1878) proved to be theday I had been waiting for. The wind had hauled to the northward during the night, and the smokehad vanished as if by magic. At sunrise, I turned my telescope in the direction of MT LOLA, andthere was the heliotrope, 169 miles off, shining like a star of the first magnitude. I gave a fewflashes from my own, and they were at once answered by flashes from LOLA. Then turning mytelescope in the direction of MT HELENA, there, too was a heliotrope, shining as prettily as theone at LOLA. My joy was very great; for the successful accomplishment of my mission was nowsecured. As soon as I had taken a few measures, I called Doctor McLean (a visitor fromOakland,CA) and (Richard) Hubbard (a guide) to let them see the heliotrope at MT HELENA,192 miles off, and the longest line ever observed over the world. In the afternoon the smoke hadarisen, and HELENA was shut out; but on the following morning I got it again, and my missionon Mount Shasta was finished. The French have been trying for some years to measure,trigonometrically, some lines from Spain across the Mediterranean to Algiers; they have onlyrecently succeeded, and it has been a source of great satisfaction to French geodesists. Theirlongest line is 169 miles. The line from MT SHASTA to MT HELENA is 192 miles long, or 23miles longer than their longest. And the glory is ours; for America, and not Europe, can boast ofthe largest trigonometrical figures ever measured on the globe. 
It is somewhat ironic that only a few years later a regular network line mentioned previously,UNCOMPAHGRE PEAK to MOUNT ELLEN was observed and at 183 miles is 14 miles longerthan the longest French observation.                                 
U.S. Lake Survey
The Corps of Engineers were responsible for mapping and charting the Great Lakes, andrecognizing that the Act of 1843 limited Coast Survey responsibilities only to the Atlantic, Pacificand Gulf coasts, setup the U.S. Lake Survey (USLS) within the Corps to do the job. Between1864-1900, this agency established primary triangulation throughout the lakes' area including anarc south from Chicago connecting to the 39th Parallel triangulation at Parkersburg, IL. 
One event of unusual interest was the several very long lines across Lake Superior they were ableto observe despite the fact they were theoretically not intervisible. While very rare, when found,these observations, known as refracted lines because the signals are seemingly lifted byatmospheric conditions so they can be sighted on, generally involve sights across water, as wasthe case here. One such line was reported in the 1930's Hudson River arc.
Special Surveys
In the 1880's, the Coast and Geodetic Survey (C&GS) offered a program to assist the states inestablishing geodetic control. As a rule, college professors directed the activities, with studentsand local people carrying out the work. Several states entered the program, but only the surveysin northeastern Pennsylvania and in New York were of acceptable quality. Other surveys ofspecial note in this period were: 
California-Nevada boundary from Oregon to Lake Tahoe and its   continuation, the oblique line tothe Colorado River  measured in 1873 by Alexis Von Schmidt, U.S. Deputy Surveyor    and thesubsequent resurvey of the oblique line by Assistant Cephas H. Sinclair C&GS between 1893-99. 
Assistant William C. Hodgkins' C&GS 1893 resurvey of the circular boundary betweenPennsylvania and Delaware originally set by local surveyors in 1760 and verified by Mason andDixon in 1763. 
Beginning efforts in Alaska over several decades, including   work on the U.S.-Canada boundaryin the 1890's.
The 1893-97 remonumenting of the U.S.-Mexico border made     under the direction of AssistantAlonzo T. Mosman C&GS.
The 1872-85(?) triangulation of the Adirondack Mountains,    NY by Verplanck Colvin,superintendent of the Adirondack and  State Lands Surveys. 
As geodetic surveying in America entered the 20th century, it did so on a solid foundation built onexcellent surveying practices where the quality of the observations was never compromised andthe quest for higher accuracies never ended.               
BUILDING THE NETWORKS 1900-1940
At the dawn of the new century, as in any year, a generation of geodesists continue to move alongthe path towards their rightful place in the profession, wherever that maybe. In the U.S. one man,William Bowie, by virtue of his fine analytical mind and determined nature emerged early as thebest of the best and in the same fashion as Hassler, totally dominated American geodesy for morethan 35 years. Born in Anne Arundel County, MD in 1872, a graduate of Trinity College,Hartford, CT with additional work at Lehigh University, he joined the C&GS in 1895. 
Geodetic Chief 1909-1936
During the next 14 years he demonstrated outstanding abilities in all phases of the bureau'sgeodetic activities, both field and office, leading to his appointment as Chief of the ComputingDivision and Inspector of Geodetic Work in 1909 (a position that about 1915 became Chief,Geodesy Division), replacing John F. Hayford, who had moved on to setup an engineeringdepartment at Northwestern University. There were several huge accomplishments during histenure and their successful conclusions can be attributed primarily to his personal involvement ineach one. 
In 1913, for example, he persuaded the governments of Canada and Mexico to adopt the U.S.Standard datum for their mapping, resulting in an entire continent being placed on one datum,renamed the North American datum, a first anywhere. In another case, Bowie pushed for thecompletion of sufficient primary triangulation in the western half of the country so that a singleadjustment could be made and once Bilby towers were available, did the same for the eastern half.At the same time he proposed a method to adjust the two halves as separate pieces, yet as a singlesystem. 
He supported leveling about equally as triangulation with the result in 1929 a general adjustmentfor the entire country was made. Also on his watch and with his complete support, the State planecoordinate system came about in 1932 and for the first time all surveyors could use the networkdata. Lastly, his grand ambition was to complete the nation's primary horizontal and verticalnetworks and for all intents and purposes he succeeded by the time of his retirement in 1936. 
Another of Bowie's interest was gravity surveys introduced in the U.S. by the C&GS in 1875which led him to become a strong and vocal proponent for the theory of isostasy, joining Hayfordin this belief. The basic principle of isostasy is that the gravitational effects of the continentalmasses above the geoid are about equally compensated for by lesser density masses below, theopposite being true in the case of the oceans. 
Bowie was recognized nationally and internationally, a founder of the American GeophysicalUnion and an early president. He was also president of the Society of American MilitaryEngineers and the International Union of Geodesy and Geophysics. Bowie was a captain in theC&GS commissioned corps, but preferred the title major, the rank he earned in World War I.William Bowie died in 1940 leaving behind a record of accomplishments that is not likely to bematched soon, if ever.
Bowie's Lieutenants
Members of the Geodesy Division making significant contributions during this period were WalterD. Lambert, Jacob A. Duerksen and Frederic W. Darling in gravity and astronomy; Sarah Beall inastronomy; Henry G. Avers, Howard S. Rappleye and Walter F. Reynolds in computations;Clarence H. Swick in gravity, astronomy and computations; Walter D. Sutcliffe in records andarchives and Hugh C. Mitchell in promoting surveys in metropolitan areas, plane coordinatesystems and authoring Sp.Pub.no. 242  Definition of Terms Used in Geodetic and Other Surveys,published after his retirement, the first and still the best of geodetic glossaries. Others in thedivision are cited elsewhere for particular efforts.
Gravity Surveys
Gravity surveys began in the U.S. in 1875 under the direction of Charles S. Peirce following theacquisition of Bessel reversible pendulum apparatus from Europe. The initial measurements withthe equipment were made at Hoboken, NJ after connecting to known gravity values in France,Switzerland, Germany and England. In 1882 international connections were made with NewZealand, Australia, India and Japan, and in 1900 to Europe again. 
Improvements were made to the apparatus by Peirce, Thomas C. Mendenhall, superintendent ofthe C&GS (1889-94) and others, the most significant being the replacement of the bronzependulum with one made of invar in 1920. Work began on the first national gravity network in1891 and completed in 1949, involving 1,185 base stations, all observed with pendulums. 
Meters Replace Pendulums
About the same time, the first geodetic quality gravimeter, the Worden gravity meter came intouse and was adopted by the C&GS in 1952 for differential measurements. Early devices of thistype appeared about 1930 for use in oil exploration and were not accurate enough for geodeticwork. The long reign of pendulum measured gravity was coming to a close after about 75 years,albeit the apparatus would continue to be used in absolute determinations for another 25 years. 
For most of the period the C&GS was the primary mover with significant contributions madeprior to 1900 by Assistants Edwin Smith, Erasmus D. Preston and George R. Putnam, in additionto Peirce and Mendenhall. After 1900, William Bowie and Walter D. Lambert led the way, withDonald A. Rice coming along after 1950 to continue their work. About 1955, plans were laid tocomplete the long desired 100 mile spacing network and to expand the existing 900,000 squaremiles of area coverage at 10 mile intervals over the entire country. 
Woollard's Contributions
Beginning in 1954, George P. Woollard began observations using quartz pendulum apparatus andWorden gravimeters to create a nationwide net and completed the work in 1958 with about 175stations established, most at regional airports. By 1963, he had extended the net worldwideinvolving some 1,300 points.
Woollard began making gravity measurements in the late 1930's, while at the University ofWisconsin, running traverses across the country and between the Gulf of Mexico andNewfoundland. He also played a part in getting S. P. Worden to build his geodetic gravimeter in1948. 
As the space age began, the need for higher accuracy gravity networks greatly increased. To meetthat requirement, the U.S. National Gravity Base Net (NGBN) was established in 1966 in acooperative effort by the Army Map Service, USAF 1381st Geodetic Squadron and theUniversity of Hawaii placing stations at airports in 59 cities throughout the country. Four LaCoste& Romberg geodetic gravimeters were used and travel was by commercial airlines. In 1971, theNGBN was incorporated in the International Gravity Standardization Net 1971 (IGSN1971)along with observations from various sources connecting stations in 36 additional cities and anumber of calibration line pendulum measurements. There are 1,854 ISGN stations, 379 are in theconterminous U.S.  
As part of the continuing effort to improve the IGSN system, the National Geodetic Survey(NGS),between 1975 and 1979, reobserved most of the NGBN using 4 LaCoste & Romberg Gmeters in a simultaneous mode and ground transportation. This new network is identified as theNational Geodetic Survey Gravity Network (NGSGN) and includes stations in 54 cities observedin cooperative efforts between NGS and other federal agencies. Calibration lines established by1990 are East Coast, Blue Ridge, Mid-Continent and Rocky Mountain. 
The general availability of geodetic gravimeters after 1960 and ease of operation has inducedother federal agencies including the U.S. Geological Survey (USGS), State and educationalinstitutions and private companies to carry out observations for several purposes, other thanexploration. Marine gravity remains a giant undertaking that continues to be pursued. A safeprediction. The last two decades of the 20th century will be known as the period when thedetermination of absolute gravity, to a high accuracy became commonplace. 
From Tables to Mechanical Calculators
At the beginning of the American geodetic experience, no mechanical calculators were availableand the computations were made using a variety of tables including logarithms, augmented by theindividual computer's arithmetic abilities. Despite of what today would be considered the mostextreme of primitive computational means, the work got done. 
The method of least squares was introduced in 1847 or 1848 and as early as 1868, adjustmentswere carried out involving closures in length, azimuth, latitude and longitude, a formidable taskeven in later years. 
Accuracy estimates determined directly from least-squares adjustments were not routinelycomputed until the mid 1960's because of the additional effort involved and other approacheswere taken to come up with acceptable substitutes. Charles A. Schott in the Superintendents'sReport for 1865, p. 192, explains the problem and the rationale for its solution as follows: Thestrict application of the method of least-squares in connection with the computation of probableerrors of the adjusted parts of a triangulation becomes, in our case, impractical from its laboriousnature, and a shorter method must be sought and followed, which, while it is a sufficientapproximation of the truth, yet furnishes us with all desirable data to judge the accuracy of ourresults. The approximations took several forms depending on the element (length, azimuth orposition) for which the accuracy estimate was desired. Most evolved from the specific conditionequation for the element and all included the probable error of the angle (or direction) derivedfrom the adjustment. That for the length eventually became the strength of figure formula, longused to evaluate the strength of triangulation and in determining the need for additional base lines.
Doolittle Makes It Less Work
In 1878, Myrick H. Doolittle made a combination of improvements to Gauss' method for solvingnormal equations that continued in general use for more than 80 years. European geodetic circlesinsisted on dubbing the method as Gauss-Doolittle and so it remains today. However, in 1924when F. R. Cholesky, a European (France), modified Doolittle's procedure, this method isidentified as Cholesky  or Cholesky-Rubin. T. Rubin, another European (Sweden), apparentlydiscovered the same approach as Cholesky, but two years later. 
Crude and cumbersome mechanical calculators appeared later in the 19th century and despite theirawkwardness reduced the task of making multiplications and divisions, the major chore incomputations. Later improvements, including small electric motors resulted in further reductionsto the computational effort and made feasible the simultaneous solution of several hundred normalequations.
Azimuths From the South - Why ?
From 1850 to the adoption of NAD83 in 1986, azimuths in geodetic surveys were reckoned fromthe south, clockwise, rather than from the more logical origin, north, used by land surveyors.Walter D. Lambert in a short 1946 article and some notes compiled in 1954 gave severalexplanations, any of which could suffice as a good reason for the practice. 
In his 1954 notes he reports that in Hassler's 1817 work and after 1832, there was no uniformity,sometimes azimuths were reckoned from the north and on other occasions from the south, andfurthermore in either direction, without any specific notation whether east or west. The remainderof the notes conclude from various writings of French geodesists of the 1800-40 period that theypreferred to measure azimuths from the south around to west and according to him so did theirAmerican colleagues. 
His 1946 article provides probably the best rationale for the practice. Lambert noted that CharlesA. Schott was a German trained geodesist and while not a student of Karl Friedrich Gauss(1777-1855) he was well aware that Gauss followed the general practice of azimuths from thesouth, clockwise, in his Hanoverian triangulation. And, further, that Schott joined the ComputingDivision shortly before 1850, was highly regarded from the beginning and it was very likely hewas responsible for the bureau adopting the practice. After 1986, azimuths are measuredclockwise from north. 
U.S. Horizontal Datums
In 1879 the first national datum was established and identified as the New England datum. StationPRINCIPIO in Maryland, about midway between Maine and Georgia, the extent of thecontiguous triangulation was selected as the initial point with its position and azimuth toTURKEY POINT determined from all available astronomic data, i.e. 56 determinations oflatitude, 7 of longitude and 72 for azimuth. 
Later its position was transferred to station MEADES RANCH in Kansas and the azimuth toWALDO by computation through the triangulation. The Clarke spheroid of 1866 was selected asthe computational surface for the datum in 1880, replacing the Bessel spheroid of 1841 used after1843. Prior to 1843, there is some evidence that the Walbeck 1819 spheroid was employed. 
The datum was renamed the U.S. Standard datum in 1901 and in 1913 the North American datum(NAD) as Canada and Mexico adopted the system. In 1927 an adjustment of the first-ordertriangulation of the U.S., Canada and Mexico began and was completed about 1931. The endresult was the North American datum of 1927 (NAD27). 
It was not a simultaneous solution because it was simply economically impractical to do so withthe available computing equipment. Nonetheless, it was the largest geodetic computation effort tothat time. More importantly, the resulting datum was the first to be oriented by Laplace azimuthsstrategically spaced throughout the triangulation. The azimuth to WALDO in the datum definitionwas changed by about 5" due to the inclusion of a Laplace azimuth at the nearby SALINA baseline. Its inclusion in the NAD27 definition was only for completeness purposes since the datum isactually oriented by 175 Laplace azimuths held fixed in the adjustment as noted previously.
Hayford Ellipsoid
In 1909, John F. Hayford using data only from the U.S. triangulation determined new dimensionsfor the figure of the earth, appropriately named the Hayford spheroid. The International Geodeticand Geophysical Union adopted the parameters in 1924 as the basis for the International Ellipsoidof Reference and it is presently used in several countries. 
Earlier he had perfected the strength of figure formula used in deciding where base lines arerequired in the triangulation. The original concept was developed and used in the U.S. Lake Survey and later improved by William H. Burger (C&GS). Hayford also was the co-author withThomas W. Wright, formerly of the Lake Survey, of the widely used text Adjustment ofObservations. He served with the C&GS for 20 years and was Chief of the Computing Divisionand Inspector of Geodetic Work for about 10 years. 
First National Accuracy Standards
In 1921 a committee decided that the C&GS nomenclature for accuracies of geodetic surveys ofPrimary, Secondary and Tertiary would henceforth be identified as Precise, Primary andSecondary. Looking back over more than 70 years it appears now to have been a politicaldecision, probably some agency objecting to the tertiary classification for their work. As usualwith such edicts, it created nothing but confusion. 
Accordingly in 1925, the Federal Board of Surveys and Maps adopted the now familiar standardsof Firstorder, Second-order and Third-order accompanied by the also familiar 1:25,000, 1:10,000and 1:5,000 length and position closures, that were reaffirmed in 1933 and remained in place until1957.
Traverse Replaces Triangulation 1917-1927
By 1900 the C&GS had observed about 5,150 miles of first-order triangulation and the USLSabout 1,650 miles. Between 1900 and 1925 about 13,000 miles of the same class triangulationwas measured in the western half of the country including the 1,460 mile 49th Parallel arcstraddling the U.S.-Canada border from the Lake of the Woods, MN and the Pacific Oceanobserved jointly with the Geodetic Survey of Canada (GSofC). 
Due to the high cost of building wooden towers, little or no triangulation was observed from1900-27 in the eastern part of the country. First-order traverse was substituted because routescould be selected along railroads, with the measurements facilitated by utilizing the rails tosupport the tapes throughout and then projecting the distances to the stations offset from thetracks. Between 1917 and 1927 some 3,300 miles of traverse were observed in 13 states, all eastof the 98th Meridian arc except for about 100 miles in South Dakota. 
After the development of the Bilby tower in 1926, survey methods for the eastern half of thecountry reverted to triangulation and between 1927 and 1931 about 9,000 miles of first-orderwork was accomplished. Among the major pieces of work completed after 1900 were the 98thMeridian arc, 1,720 miles in length observed 1897-1907; 49th Parallel arc, mentioned previously,about 1,460 miles long measured in 1924 and the last of the great triangulations, the Atlanticcoast arc, perhaps 1,600 miles in length from Providence, RI to Key West, FL completed in 1932. 
NAD 27
In the adjustment that created NAD27, all the first-order triangulation and about 100 miles offirst-order traverse for a total of 15,050 miles were included in the western half computation. Forthe eastern half adjustment only the triangulation west of the Eastern Oblique arc amounting to11,850 miles was used including USLS (1,650 miles) and GSofC (630miles) work, but none ofthe first-order traverses. Other omissions were: International Boundary Commission(IBC)-GSofC triangulation observed before 1920 from Lake Superior westward to NamakanLake (about 200 miles) because the connection to the 98th Meridian arc was a first-order traversemeasured on the frozen Rainy River in Minnesota and a 200 mile section of the Mississippi Riverarc from St. Louis northward completed in 1931, possibly because the records were not yetreceived. The work to the east of the Eastern Oblique arc, including the entire Atlantic coast arcand other triangulation in parts of Virginia, North and South Carolina, Georgia and Florida wasleft out because traverses were involved. 
By 1950 it was evident that NAD27 had many problems caused by large loops in the west and aninsufficient number of base lines and Laplace azimuths. Estimates made then suggested that halfagain as much of the 26,900 miles of triangulation included in the computation and twice as manybase lines (112 included) and Laplace azimuths (175 included) would be needed. 
By 1940, this amount of new work was largely available, made possible by civil works' fundsallotted to aid the unemployed, but no one in 1927 foresaw this happening. Hindsight, of course isalways better than foresight. 
Reconnaissance Surveys
Reconnaissance surveys, the in-field planning and selection of locations for triangulation stationswere always part of geodetic operations in the U.S. However, it didn't become a separate anddistinct function until the 1880's when multiple observing parties began to come on the scene. Upto then, there was only an occasional need to plan more than a few figures ahead and this couldeasily be done by the units as work progressed.
The strength of triangulation depends solely on well-shaped triangles and sufficient redundantobservations to verify the acceptability of the angle measurements. The latter was the basis foradopting the specification, during Bache's time, that all triangulation was to consist ofbraced-quadrilaterals and/or central point configurations.
How High is Enough ?
Fulfilling these basic criteria often required towers for intervisibility and deciding on their heightswas a problem within itself. Prior to Bilby towers, the cost and time needed to erect woodensignals was a major factor for making an additional effort to assure that a minimum height wouldsuffice. Profiling lines by various means, including the determination of elevations from verticalangles and estimated distances, and by barometric observations were common solutions to theproblem at all times. The effect of the earth's curvature and refraction often had to be worked intothe equation, as well. For examples: On a 10 mile line, absolute flat terrain, 15 ft. towers at eachend, or 58 ft. at one end, would be required for minimum clearance; and for a 20 mile line, samesituation, 58 ft. at each end, or 230 ft. at one end.
There were two schools of thought, however, on how extensive the profiling effort should take.One side contended that regardless of the effort, blocked lines would happen, and the usualsolutions, raising the heights of towers or adding another station would be less costly overall.Others thought otherwise. And many who traveled some distance to reach the station site, only tofind a line not visible, would agree with the latter.
The Job Entailed
Selecting base line sites and planning the base expansion net to the triangulation was anotherresponsibility. Depending on the length of the base that could be accommodated by the location,the connecting figure had to be very carefully chosen, so as to minimize the number of observedangles involved in the expansion of the distance, and that they would be the strongest possible.Prior to the availability of EDMI, the ratio of triangulation lines and bases was about 3:1 on theaverage, albeit some approached 10:1.
Traverse, unlike triangulation and trilateration, has no strength of figure per se, and the generalinstructions were to select points about equally spaced and in a straight a line as possible. Morefrequent astronomic azimuths and positions, than required for triangulation, were observed tohelp control sway in the survey.
In addition to selecting the station sites, lines to be observed and height of towers required, thereconnaissance engineer was responsible for preparing a sketch showing that information, ties toestablished control and marks of other agencies, and topographic features such as landmarks thatmight serve as intersection stations. Also, prepare descriptions on how to reach the proposedstation sites, recovery notes for old stations,indicate types of marks to be set at each station, setupcontacts with public officials and property owners and specify any arrangements made with theowners in regard to crop damage, etc.
Party Makeup and Can Do Spirit
Reconnaissance parties generally consisted of a Chief of Party (Assistant prior to about 1910),one or two assistants, and the necessary vehicles and equipment, usually an absolute minimum. Asa case in point. In 1911, Jasper Bilby and one assistant ran the reconnaissance for the 104thMeridian arc from Colorado Springs, CO, to the Canadian border, about 720 miles, in a little over3 months, selecting sites for 74 primary stations, 23 supplementals and 2 base lines. Hisequipment was 3 mules, 1 wagon, 1 riding saddle, necessary tools for repairing the outfit, 1 tent,cots and bedding for 2 persons, and a few cooking utensils. He also had a 4-inch surveyor'stransit, a prismatic azimuth compass, a field telescope, binoculars, a set of drawing instrumentsand all available maps.
In later years, trucks were substituted for the mules and wagon, and living conditions weredifferent and usually better, but all else, including the work itself, remained substantially the same.GPS changed all this and reconnaissance surveys are considerably simpler today, nointervisibilities required for example, yet geometry and other factors are no less important thanpreviously.
No formal reconnaissance was usually made in leveling. Bench mark setters selected the locationsand set the marks, at intervals as called for by the project instructions, sometime prior to theobservations.  
NOTE: (C&GS) following names, for events after 1920, indicates they were commission corpsofficers at the time.
Alaska - Hawaii - Philippines
By 1940 first-order triangulation on NAD27 had been extended to Skagway in southeast Alaskaand earlier in the century first-order surveys from Shelikof Strait to Cook Inlet to Anchorage andon to Fairbanks were completed on an independent datum. Lower-order surveys computed onseveral independent datums covered much of the coastal areas including the Aleutians. In 1943Skagway and Fairbanks were connected by first-order triangulation bringing NAD27 to the mainland mass, albeit it would be more than a decade before all of Alaska was on a single datum. 
Between 1900-40 geodetic surveys, mostly second-order triangulation, were established in thePhilippines, Hawaiian Islands, Puerto Rico-Virgin Islands and the Panama Canal Zone withpositions based on datums specifically developed for each region.  Surveys of the islands west ofHawaiian chain, including Midway were based on local astronomic datums. Surveys on MidwayIsland were completed late in November, 1941 and personnel were en route by C&GS ship toPearl Harbor on December 7, 1941. Their arrival was delayed due to running zigzag coursesunder radio silence causing a fear for several days that they had been lost in the first actions of thewar. 
Most of the work in Puerto Rico and the Hawaiian Islands was upgraded in the 1960-80 period.During the same time frame, new surveys were carried out on Guam, American Samoa and for theDefense Department, on Kwajalein in the Marshalls.  
The Philippines presented a unique situation because of the agreement that 50 years after the warended in 1898, the islands were to become an independent nation. The role of the C&GS wastherefore an advisory one to the Insular Government and to this end about 1906 a processingoffice, including computations and map making functions was set up in Manila. All the geodeticrecords were held there and only the lists of adjusted geographic positions were furnished theWashington office. 
Much of the geodetic work, primarily second-order triangulation, as noted earlier, including theconnection to the British surveys on Borneo, was completed when the war began in 1941. Anextremely difficult task to accomplish because of the tropical jungle, mountainous terrain andoccasionally hostile natives. 
The processing office was taken over by the Japanese early in 1942 and destroyed in 1944 duringthe retaking of the islands, with a loss of most of the geodetic records. George D. Cowie(C&GS), in charge of the office was killed in the bombing of the city on Christmas Eve, 1941, andseveral C&GS employees and a few families were imprisoned by the Japanese for the duration.One prisoner, Joseph W. Stirni (C&GS) was killed in 1945 when a ship taking him to Japan wastorpedoed. Two others, Clarence F. Maynard, a civilian mathematician and George E. Morris(C&GS) were captured on Bataan, survived the Bataan Death March and imprisonment in Korea.Maynard returned to the Philippines after the war, remaining until all C&GS personnel wererecalled in 1950. On his return, he was Chief, NY Computing Office for several years. 
Earthquake Investigations
Following the 1906 San Francisco earthquake, a selected scheme of triangulation from Montereyto Fort Ross involving primary, secondary and tertiary stations and a detached net of tertiarypoints at Point Arena were reobserved to determine the amount of crustal motion. This was thefirst time in the U.S. that triangulation was reobserved for this purpose. Displacements werecomputed for all points in the disturbed area resulting from the 1906 event and where possible forstations effected by an earthquake in 1868 also. 
Between 1922-24, the primary triangulation from Lake Tahoe to San Francisco to Santa Barbaraand eastward to southern California was reobserved for the same purpose. Extensions werereobserved in 1924-25 northward to Point Arena, east to Carson Sink, NV and to westernArizona as further verification of stability of the terminal points. 
One special point of interest arose from a discussion of the computations. Arthur L. Day, Directorof the Carnegie Institution's Geophysical Laboratory wrote to Bowie and Walter F. Reynolds,Chief Section of Triangulation, in 1931 supporting a suggestion made by a reviewer of the results,Harry O. Wood in 1930 that circular errors, representing the precision of the observations bedetermined in the adjustment and shown on the sketches with the movement vectors. The requesthas to be among the first anywhere for such information. Both nicely sidestepped the issueknowing full well determining such estimates was impractical at the time, especially so becausethe C&GS used the method of condition equations for their adjustments and that method was theleast amenable to providing such data. In fact no method could readily do the job then. It wasn'tuntil about 40 years later that circular errors and error ellipses were routinely computed.  
Other crustal movement resurveys included the 1929 Newport Beach to Riverside arc, CAfollowing the Long Beach 1933 earthquake with little movement indicated. Also, during the1930's several lines were releveled in San Francisco, San Jose, Los Angeles and vicinity, SanDiego area and the Imperial Valley, CA, with all showing some displacements. One or two arcsand a number of level lines in California and other parts of the country were observed specificallyfor future crustal motion studies.    
Speed of Light
In 1922-23, the most accurate invar taped base line ever, with a precision of 0.2ppm one sigma,was measured near Pasadena, CA. The sole purpose for the 20.9 mile base line was to provideAlbert A. Michelson with the best possible distance between points on Mount Wilson and SanAntonio Peak used in his experiments to determine the speed of light. 
To assure the  least loss of accuracy in projecting the measured distance to the line between thetwo points, the base was measured parallel to that line and to its approximate length. Astronomicpositions were determined to correct the angles for the deflection of the vertical. The work wascarried out under the direction of Clement L. Garner (C&GS), later to succeed William Bowie asChief, Geodesy Division. 
Bowie and the C&GS were interested in Michelson's experiments in the hope that means could befound to measure distances using light. It was not to be. The experiments were not totallysuccessful and the Great Depression began, leaving Erik Bergstrand to develop the equipment 25years later, in Sweden. 
The 1938 AMSTERDAM Avenue base line in New York City presented a similar problem, buthere the stations were atop high buildings. It was necessary first to project the base vertically totemporary points offset from the stations and then a lateral shift to the station marks. 
Early Urban Surveys
Between 1903-08 a first-order triangulation network encompassing greater New York City wasobserved; Cincinnati did the same on their own in 1912-13 with Hugh C. Mitchell, on assignmentfrom the C&GS in charge and in the mid 1920's, combined first-order triangulation and traversesystems were established for Rochester, NY and Atlanta, GA. These were the forerunners of thenumerous State-wide, county and urban nets observed later in the century.  Prior to 1940, severalcities developed networks on their own or with private sector assistance. As a case in point,first-order control surveys and associated topographic mapping for a number of municipalitieswere accomplished by the R.H.Randall Co. of Toledo, OH between 1920-34.
Tangent plane coordinate systems, most at ground level, were setup for these early urban surveys.After the advent of the State  coordinate system,only the Cleveland Regional Geodetic Survey(CRGS) adopted a tangent plane ground level grid.
SPCS - UTM and Oscar S. Adams
In 1933-34, Oscar S. Adams ably assisted by Charles N. Claire developed the State PlaneCoordinate System (SPCS) at the request of George F. Syme a North Carolina Highway engineer.Syme died shortly after the North Carolina system was developed being succeeded by O.B. Bestorto carry on the cause. Bestor was in charge of the State local control project established in 1933,later identified as the North Carolina Geodetic Survey. Most State and the few county projectsinvolved in this program also were so named. Colonel C. H. Birdseye of the USGS, with a stronginterest in Statewide coordinate grids also participated in the several conferences leading to thedecision to honor Syme's request. 
The first tables for computing Lambert coordinates were developed for North Carolina and thefirst tables for the transverse Mercator grid were for New Jersey. Tables were prepared for allStates early in 1934. For the first time all horizontal control stations previously defined only bylatitudes and longitudes would be available in easy to use plane coordinates. 
Adams had many notable accomplishments prior to this work. For example, he authored orco-authored 22 Special Publications and Serials dealing mostly with map projections andadjustments. This group includes Sp.Pub.no.28 Application of the Theory of Least Squares to theAdjustment of Triangulation issued first in 1915 which provides the mathematical basis foradjustments by condition equations and observation equations on the ellipsoid and still remains aviable part of the literature. 
He was actually the father of NAD27 since he gave Bowie's adjustment proposal life andpersonally made many of the computations. Later he was directly involved with the creation of theUniversal Transverse Mercator (UTM) system used by the U.S. Army worldwide, although hisassociation with the project is not well known. Adams also collaborated with Bowie in 1918 indeveloping the Military Grid System, the forerunner of UTM, dividing the country into sevenzones, 9 of longitude wide, with the polyconic projection the basis for the grid.
Great Depression Surveys
The 1930's saw a huge increase in funds for public works as part of the effort to get the countryout of the Great Depression and the C&GS field and office staffs were significantly increased. Atthe height of the program more than 1,000 employees were in the field and as many as 12observing units, from a single party were working some nights. 
For the first time ever a number of second-order arcs were observed by geodetic parties, bringinggrumbles from purists and rightfully so, the savings in time and effort were very small. In additionabout 23 States and a few counties setup geodetic surveys, under the overall supervision of theC&GS, with the intent to establish second-order horizontal and vertical control at the local level. 
In the earliest stages all States participated and more than 10,000 unemployed surveyors,engineers and technicians were given meaningful jobs, albeit the pay was less than $20 a week.Most of the 23 geodetic surveys accomplished some work although only a few made substantialcontributions. Among those that did were: Alabama, Florida, Georgia, Louisiana, Massachusetts,New Jersey, North Carolina, Oklahoma, South Carolina and Tennessee; among the counties:Monroe and Westchester in New York and the regional geodetic survey in Cleveland, OH. Exceptfor Massachusetts and Westchester county, where first-order triangulation also was observed, allsurveys involved traverses. 
Whether the expenditure of the funds had the desired overall economic effect is still beingdebated, however there is no doubt the funds spent were highly beneficial to the geodetic controlprogram as many thousands of new stations and bench marks were established. To wit, there weremore than 100,000 points of all orders of accuracy in the horizontal net by 1940.
Geodetic Leveling, Datums, and Instruments
Geodetic leveling has always played second fiddle to horizontal surveys. Perhaps this is sobecause leveling is perceived as a simple procedure, although it most certainly is not. Some formof leveling, mostly trigonometric in nature was always observed in order to provide elevationsneeded to reduce base lines and angle observations to sea level. As a matter of fact, theobservations were often carried out as a separate event using specially constructed vertical circleonly instruments. 
As work on the Transcontinental arc progressed westward it was recognized that vertical angleelevations would not be of sufficient accuracy for the purpose. Accordingly a line of precise levelsfollowing the route of the triangulation was begun in 1878 at the Chesapeake Bay and reachedSan Francisco in 1907. 
In 1898, an adjustment was made of the first 25 circuits and a second in 1903 to include the largeamount of new data observed in the interim. Partial adjustments were carried out in 1907 and1912 to include the ever increasing work. In 1929 a general adjustment was made which included45,000 miles of U.S. first-order leveling and 20,000 miles of similar accuracy Canadian surveys,with sea level planes at 26 tidal stations held fixed. The Canadians had recently published theresults of their observations and didn't accept the combined adjustment values. Difference ofelevations at common bench marks didn't exceed 0.5 ft. The U.S. data also includes preciseleveling observed by the Corps of Engineers, U.S. Geological Survey and other organizations. 
By 1940, about 260,000 miles of first- and second-order leveling had been observed. Theelevation datum was known as the Sea Level Datum of 1929 (SLD29) until 1973 when the namewas changed to the National Geodetic Vertical Datum of 1929 (NGVD29).
Prior to 1899, geodetic leveling in the U.S. was observed using wye levels and target rods. Longtelescopes were common to such instruments and critics claimed Americans bought their levels bythe yard. In 1899, the Fischer level designed by Ernst G. Fischer of the instrument division, adumpy type and speaking rods replaced the earlier equipment and were used for almost 70 yearswith only slight modifications. Invar strips were added to the rods in 1916.
Mt. Whitney - Precisely How High ?
Elevations of high mountains are rarely determined by spirit leveling, most being the result oftrigonometric methods, a k a zenith distance/vertical angle elevations. As a matter of fact, thehighest mountains are seldom occupied for horizontal positioning either for obvious reasons,clouds and weather conditions among them. Despite these negative possibilities, in August 1925,Lansing G. Simmons (C&GS) was sent to Lone Pine, CA to observe first-order leveling frombench marks on the Owens Valley line to the summit of Mount Whitney, the highest peak in thethen 48 states. The purpose was for crustal motion studies where future relevelings would giveindications whether the mountain was growing or not.  Since it was late in the season, Simmonsdecided to level from the summit down, but found the summit trail from Whitney Portal, about 14miles west of Lone Pine, blocked by rock sides and learned furthermore that no horses had beenover the route in several years. He then decided to horsepack the outfit to Army Pass at anelevation of 11,000 ft. about 10 miles south of Mount Whitney, from where the party wouldbackpack the equipment to a base camp at 14,000 ft., about one mile south of the summit. 
Despite some of the 8 man party suffering from the altitude, that was further compounded byliving in pup tents, with the only water from melting snow and the only fire from a gasoline stove,they were able to complete the leveling from the summit, marked by a USGS disk set in 1901, toa permanent bench mark near the base camp in a week's time, a vertical distance of about 500 ft.Bad weather set in with snow, hail, cold and high winds and there being little chance withSeptember approaching for better conditions, the camp was backpacked to Lone Pine Lake nearWhitney Portal at an elevation of about 8,400 ft. where the leveling was picked up again for the13-14 miles into Lone Pine. 
Two years went by without the Forest Service or local people clearing the trail to Mount Whitneyso in June 1928, John H. Brittain (C&GS) was ordered to Lone Pine to form a party, completethe first-order leveling from Whitney Portal to the summit and with authorization to open the trail.He made his first camp at the 10,400 foot level, opened the trail to 11,500 ft. taking only one dayto do the job and completed the leveling to that point. From a second base camp at 12,000 ft.,leveling was run to the summit marked by the USGS tablet described earlier by Simmons. Thiswas a remarkable piece of work. To carry the elevations over a vertical distance of 6,126 ft. andextremely rough terrain in 18 days of leveling required determination and esprit de corps thatwould rarely be found today. 
No resurvey has been made to date. Simmons and Brittain went on to long and distinguishedcareers in the C&GS. Simmons was the Chief Geodesist for about 20 years, retiring in 1967 andBrittain at the time of his retirement in 1961 was Chief, Geodesy Division. Lansing G. Simmonsdied in 1986, at age 84. 
The experience here seems to have discouraged further attempts to level to the summits of highpeaks even when roads are available such as to Pikes Peak and Mount Evans in Colorado, bothover 14,000 ft.  However, with increasing interest in replacing conventional leveling with GPSobservations, the tests presently underway (1994) might consider including first-order leveling tothese and other readily accessible peaks as part of the examinations.
As geodetic surveying in the U.S. entered the fifth decade of the 20th century, the first-ordertriangulation and leveling were basically complete. Future priorities would be to fill in the gaps,strengthen and update the networks and carry out new adjustments of NAD and SLD (NGVD).All would come to pass and much more in the next 50 years.  
This brief and informal history of U.S. geodetic surveys covers the more significant happeningsplus a few of the more interesting incidents in the period 1807-1940. The decades to follow wouldbe a most dynamic and amazing era as the surveying world would ever see with newinstrumentation, methodology and computers eventually dominating the scene.