Richmond enquirer. [volume] (Richmond, Va.) 1815-1867, 1816-12-07

whole state being divided into i,iangies cor
nected with each other, the actual position Oi
the angular points OF all these triangi2s may be-
asceriin2d, without any other measurement
than that OF the original base line
Different means, however. have been en-
p0ycd III ths calculation az the sides 81. these
ttiangles ~ different matieinatcinEs. Some
compute Tie sides and angles OF all the trim
giles ny the rtics icslirlsonOme,ry. Ota-
ersa-i.n reduce the observed angles tosui,:es ct
TIE chords OF the respective arches, &caicuiate
(3y PLAIN triSononetry)iiOnl such reduced am
giles aud thcir chords The greater number OF
the best practical mathcmaticials prefer "a mode
founded upon the following curious and siogu-
lar theorcrn, which WAS first demonstrated by
w. f-cgendre M ,he memoirs of the Paris Acad-
envy Tor 1885,
6 4 spherical triaagie being proposed, of ,rhich
the sides are rerg sDaH compared teift tie raiisS
Of TIE sphere y from eich 0f is ans les Oge thsioC
the e1ceSS Of the Srn 81 ITS three g,cS Gbors tao
reht oagies be sa5trdcteI tke aas SO Diminished
may BE- taken for the angles of ,,e inc0,. trim
gle 'chose sides are eqaai "a !eagl to thos. Of the
proposed y2herico! Triangle
AS the correctness ola chart formed upon
Observation-Disclosures depends entirely upon
tue accurate measurement OF the original base
line, the greatest attention ought To be paid ia
selecting proper instruments for this purpose.
Generat Toy, who superintendent the survey OF
q. Britain, commenced his measurement at
Hounslow Heath with deal rods, each of 20 feet
In length. Though they, however, were made
OF the best seasoned timber, were perfectly
straight, and were secured from bending in the
most etiectual manner; vet the cliaupesiu their
lengths (occasoned by the variable moisture s.
dfyness OF the air. were so great, as to take a.
way all confidence in the results deduced from
them; afterwards, in consequence of having
found BY experiments that solid. bar of glass
| IS more diiatable than tube of the same mat
Ter, glass tubes were substituted for the deal
rods They were each 20 feet long, nclosed in
wooden frames, oas TO allow only OF expansion
or contraction in length from heat or cold ac-
The base measured with these was found 10 be
DID miles. Several years afterwards, the
same base was re-moasured by Colonel Nudge
with steel chain l01 feet long, constructed by
RdnSden, and lointed like watch chSin This
Chain was always stretched TO the same cXtensi-
on, supported on troughs laid HORIZONTALLY and
allowances were made for changes in length by
reason of variations of temperature at the rate
of .0O1J of an inch tor each degree OF heat from
GO OF Fahrenheit the result of the measure
ment BY the Cham was found not 10 differ more
than Il inches, from General Roys dctcrminati-
on, by means of the glass tubes
The French matheinaticians in their trigono-
metrical surveys, employ BOrda' srepeatmg cir
Giles, instruments which are extremely portable
and which can take angles within one second OF
two seconds of the truth. The only objection to
them is the small telescope which is alta ched 10
them, whose magnItying power is not sufficient
TO distinguish accurately distant objects Ge-
neral Roy and Colonel Nudge both used Rams
dens iheodoiiie, which is provided with tel
As a striking proof OF the accuracy OF the sur
vey of gland, which was done III this manner
General Roy, who first measured the base on
Hounslow Heath, measured another on the HAT
ground OF Romney Marsh, in Kent, near the
Southern extremity of the first series of trian-
giles, and at the distance imore than 90 miles
from the first base. The length of this base Of
verihcation, as actually measured compared
with that resulting from the computation, thro'
The whole series OF tiiansles, differed only b.
% inches.
ispian bytrigonometricalsurvc | should
propose, not only as the most accurate which
could be pursued for obtaining a correct map
OF the State of Virginia but as also theleast eN-
pensive-for, am confident, IN active survey
or, with competent aids, MIGHT accomplish the
business for $1,000.
If this plan, likewise, should be deemed oftoo
extensive 4 nature TO he entered into at pres
ent, the next most eligible mo lie q of opini-
ON would be to ascertain with precision the Ia
ttude and longitude of the courthouse OF eve
ry county in the State also, the latitude ~ lon
gltude OF all the conspicuous points which ma
ture has marked out--lChe position of these be-
ing determined, think map Sufficiently cor
rect tor every ordinary pufpose) might be made,
without any other aid than those charts already
in existence, and information carefully collect
ed troUi the surveyors of each county
AS to the most correct and expeditions mode
OF determining tine ATTITUDES and longitudes,
Know OF none better In the present instancsJ
for the latitude, than observations of the celes-
tlal bodies by good Hadieys sextant; and for
the longitude, an acromatic or rejecting teles-
cope of sufficient power to determine with pre-
clsion the time of the eclipses OF the satellites
of Jupiter.
A variety of instruments and means are fire.
quently employed in determining with accura-
cy the latitude and longitude OF places ; but a
good observer, furnished with those | have
mentioned, have no doubt would answer ev-
cry purpose required.