The Roanoke times. [volume] (Roanoke, Va.) 1890-1895, 1892-01-14
THE CITY SURVEY.
a Detail Statement of the Work Already
Completed.

|t The most satisfactory piece of work
that has been accomplished in the city
engineers Office for long time is that
done on the city survey.
MIR. George 2. Wood is the engineer
dn charge of the survey, and he is at
tending to tho minute details in most
careful manner. The triangulation was
completed in December and the force
has been engaged during the present
month in copying abstracts and check
l ing up the work.
L The entire system is composed of
II twenty quadrilatorals and thirteen
triangles. These are formed by COM
bination of fortysiX stations that will
1 hereafter be referred to by number.
4 Tho main system consists of stations l
A to Is, inclusive, "a to 81, inclusive, and
] 40 and AZ, inclusive. Station o is on
tho roof Of the Hotel Ponce de Leon,
and stations, 13 and 90, were elevated
temporarily for purposes of observation.
For convenience several of the stations
were located upon high ground little
outside of the corporation. With two
exceptions the triangulation monuments
consist OF sin. copper wire inserted
in the top of a granite block exc inches
x2 feet, and held in place with lead
The exceptions are at 0, where copper
tack in tho roof of the Hotel Ponce de
4 Leon, and at 10, where copper wire
4 inserted in the native rock, designate
the points.
Three base lines, situated at the
!, eXtremities of the main system, havo
been measured These have been
named with respect to their positions
! tho south, east and west basis. great
i deal of prccaution was taken in the
rp,0u 90
j these measurements were made during
gentle rain storms, the temperature,
which was nearly stationary, being
carefully noted. The tapes, during the
y measurement, were suspended in hooks
a at intervals of 30 feet and were sub
y 1ected to tension of 16 pounds, applied
4 by motion of a screw and measured with
81 spring balances.
4 Station 81, situated north of Eighth
Il ave .ue 8. w. and in tho line of Com
81 merce street was selected as the most
81 convenient place to take the observa-
A lions necessary for the establishment of
4 true meridian. The latitude of Roa-
y noko was determined from the most &C.
& curate map at hand-from q map re-
81 ceived from the United States Geologi-
Zeal Survey-and, roughly, by an obser-
q walton on tho star 81 Cephei; all of which
81 agreed within limits, so far as it's effect
q upon the determination of the meridian
Ais concerned. The azimuth of the line
S $40 was determined by eight observa-
Il tions. both direct and reverse, upon the
#star Polaris at eastern elongation. The
= weighted mean of these eight observa-
81 tions was used. The bearing of this
q line is found to be north i've degrees,
S2eleven minutes forty nine seconds west.
81 The station "a has been assumed to be
N oot IA
81 the origin of co-ordinetes.
y The method of observation gave rise
81 to certain rigid conditions, to be full
&filled by the angles bout the stations.
S3These conditions are that an angle must
"a be equal to the sum of its parts and the
28sum of the angles about the station
amust equal $50 degrees. The adjust
&dment of the angles to fulfill these condi-
So lions was accomplished by the method
8of least squares. This adjustment gave
#rise to some very tedious computations
#The use OF quadrilaterals, of which the
8system IS mainly composed, has given
8rise to more rigid geometrical condi-
&tions than could have been secured by
Mother means. The conditions used in
III the adjustment, which was also made in
3i3accordance with the method of least
88squares, were that the sum of the an
I{gles of each triangle into which quad
ArilateIal is divided by its diagonaIs is
#eHual to $50 degrees, and that the sines
81 Il all the angles of these same triangles
<Amust be proportional to the length of
S$the opposite sides.
81 The length of sides has been COM
&puted by the sine ratio, all computations
Sabeing carefully checked. The latitude
3pnd departure Of the various parts Of the
have been computed, and from
shat the rectangular co-ordinates of the
Ea6tations. The discrepancies in the sys-
$zRem have been adjusted out, and the en-
93kIre system is now geometrically con-
iistent. a complete record of all adj
adjustments and computations has been
Except in a special book for the purpose.
"a The accuracy of the system mas re-
efeived many very severe tests. Of
$these the following are of the most
mportant: The length of the east
#base, as computed from the west base
$#hrough the main system, varies from
Its measured length by 0. 1877 feet, which
lis to the length OF base as one in l4,l2S.
5Hrhe length Of the south base, as COM
buted from the west base, differs from
Its measured lengGh by O.012 feet, which
s5js 20 the length of base as one in S9,99S.
3a$he ratio Of these errors to tho outside
berimeters of the system through which
The computations extend is one to
:il7. $50 and one to 4,035,394 respec-
#ively. Another significant check was
An the location of station l6. The CO.
|Srdinates Of this point, as computed in
3he main system from tho west base,
f iffered from its location, as computed
aS7fom the same base through the north
28}hain, by OTIS feet in departure, and by
m .O3O feet in latitude.
The successful completion of the tri-