The Houston daily post. [volume] (Houston, Tex.) 1886-1903, 1901-09-30
BY STARS AND CLOCKS.
How Longitude Is Ascertained by the
United States Government
STARTING POlNTSATEIGHTEENs STATIONS
A Simple but Delicate Operation Just
Finished at Observation-Disclosures
inu Massachusetts and Wisconsin.

Cambridge. Mass. September '2s Rough.
~ speaking. the longitudc-as well as tue /
latitude Of every town and village on the /
map has been ascertained As matter |
OF fact, however in the whole United |
states less than 200 placcs-of witch cam
bridge, where the dome Of the Harvard |
observatory appropriately marks the true
meridian was the first located with !
astronomical precision. Eighteen Of these /
are the starting points from which the true |
longitudcs OF the other places VI the list |
have been determined. These eighteen sta
lions, on which all the others depend, |
together constitute great systcm--wurked /
out station 10y station by the United states /
coast and gepdetic survey Which Is KNOWN !
States" The method by which this net |
has been established was developed by the |
United States survey with the assistance |
of the Harvard observatory, Immediately |
after the Invention of the telegraph hAd |
made the undertaking possible. The pres |
ont accuracy OF the system. however was
thirty years ago, had brought GrcVnWtrh, I
the zero or starting point OF an ionglluli- |
nal measurement, IA direct conneStion Win |
some point IN lhlS country. rms point |
was naturally the Harvard observatory, as !
being the nearest important ASTRONOMICAL
station ON this side OF the water, and the
bridge and Greenwich is still the link on
which the validity Of the whole net, In
Washington Key West, Minneapolis uma
ha. San Francisco. New Orleans, Calves
ton, or Calais, Maine. depends.
II will hc seen, however, TINT no ono
station of the net is superior to the othcrs
as a standard meridian, although the d's
tinction is sometimes accorded to Washing
ton. At first. of course, the Harvard ub-
serNatory was the only standard in TINS
country, because az that time no other
meridian had been so accurately deter
mined and 1t is historically of importance
as being the foundation Of the whole sNs-
ten as now accepted. But the government,
when II Is necessary 10 locate exactly some
approx imate, takes the nearest point In
the longitude net as It's basis of reference.
For this reason aud not because II was
the primary point In the systematic Cam
bridge o scryatory has recently been made
the basis for determining the true longitude
Of ProNiuCetoWu, AT the end of Cape Cod,
by series of observations which are IN
| teresung' not only as an example OF me
tClcgrapldc method 10y which all such work
rs conducted, but ms a step In the working
out of an extensive geadctic problem
Al first glance the determination of the
cNpct Longitude Of ProvinCctowu, ana later
of the latitudc-whch is obtained on tle
spot, without reference to any other place
would setH to be OF local rather than Ma.
udnHi importance, In reality, however,
the location which II already had was quite
sufficient for all needs Of its own The
I little Cape Cod town one eul Of grent
arc crossing more than a third OF the cor
ilnent and ending, probably at Fcnnlmore
which will he determined later on from the
standard meridian Of 0mahn. This are,
like the great American are Of the thirty
ninth parallel OF latitude, the largest ac.
curAtelN surveyed and measured strip of
land In the world. stretching as IL does
from New Jersey to California. is TO be
/ used as measure IN determining the
dimensions Of the earth: and now lacks
only the Wisconsin end to make II com.
plete from Massachusetts Nesl ward, tho
/ necessary intermediate points having al
. ready been calculated.
The Theory OF determining the longitude
! Of ono place from The known longitude OF
another is simple although the actual per-
| Torrance Of the work requires years u
| training and Instruments of the utmost del
! icacy As everybody knows, longitude Is
| the distance Of q meridian. In this case
Ifhdt OF Provincctown, from the meridian
! Of Greenwich, measuring the distance eth
! cr in degrees. minutes ana seconds OF space,
| or In degrees. minutes ana seconds Of tmc.
| If, for example one supposed q star in
! the meridian of Greenwich, the difference
In longitude az ProyiuCctuWn would be the
time that would be required In the daily
| revolution Of one earth from west to cast
! to bring the star on the meridian Of Prov
| iucCtowu; aud i'm The same way II The star
Is first imagined on the meridian OF PROV
incctuwu The time required by The rCyolu-
] tlon of the earth to bring the stu over the
meridian of the Harvard observatory MS
the nearest uHlNEulNNl lnNlluIIN NhNU Ht
i che difference IN longitude between l'toy
I inccioWu aud Cambridge The difference
ln longitude lis thus exactly measured 10y
the difference IA Time ana the problem
involved is simply the determination OF
this time difference not by O comparison
| Of watches. but hy comparison Of the
local rldorial, on star, time taken al boih
| stations from the same stars
In the actual work the two stat0nS-one
| with the known. the other with the uu-
4 known longitudc-hHd the same equipment
d.
of the United States coast and geodetic
survey In tic observatory In Cambridge
was the same as that set up by his fel'
low observer, Mr. W. II. Fairfield. in the
temporary observatory at Province own.
the only difference being In the movement
of the two chronomcterS which are iu-
cvftably subject 10 slight inaccuracies when
compared wi,a the movements NJ the time
" stars chosen for observation. 10 correct
4 these iuaccurAcieS which might have been
disrcgaded In anything less delicate thnn
Astronomical observation WAS. In short,
the important purpose Of the work under
taken not only 10 correct l'oth clocks, pu'
TO compare thc corrected dine AT the same
| instant without allowing elthcl llh'pltct
| to become once more lnhultrSm1uE mac
curate. 10 accomplish this two observers
two similar sets OF delicate Instruments
full after-reckonlngs +" eliminate even lhe
= time taken up 10y the transmission OF q
Z telegrAphlc message. were all required
The apparatus consisted Of u transit toi
! observing the stars, chronomctef 10.
keeping the local lime Of the observations
chronOgraph for recording the exact m
slant when each star crossed the mefid
ian. and a tclegraphic switchboard b}
| means Of which the Cambridge and Prov
lncetown obseryatorles were Kept in direc
communication and the observations a.
each recorded on both chronogrnphs. Oh
these lnStruiSsnts the transit may 10
! roughly described as n telescope 80 mount
ed that II sweeps great half circle Of
the heavens. keeping always IN the plane
Of the meridian. to which IL offers hel(
crossed by eleven hair lines over which
the. transit OF star may be exactly noted
n The chrOnOgraph Is revolving roller OF
which n fountain pen, operated by elec
| trlcal connection With the observatory
chronomcter. draws straight line marked
! Into seconds as second by second, th'
chronomrtcr makes and breaks the cir
cult This pen Is controlled also by tele
graphic key, touch on which records 81
the rhronOgraph the exact moment wheI
the star crosses each line INTO which TN
held rs divided.
Twenty stars the usual number, wer'
chosen for observation, IN sets OF ten each
OF these stars siNteen-that is 10 say, fou
/, Ia each group OF hve--were time stars,
chosen because Il was already known iron
the publications Of the naval observator.
al Washington and from Greenwich, a
what moment each would culmnnie.o
az q