The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1856-1888, 1883-06-30
Pendulum Observations.

These observations were COMMENCED on
Tuesday night IN Ihe basement Of the y II {.
A.. building Jy M. E. D. Preston Of the q. :.
Coast Survey and Lieut.. 5. J. Brown Of the L.
;. Navy.
The final objects OF these experiments Is TO
determine the shape OF the earth; 70 10 this It
Is necessary 70 determine the force Of gravity.
and this method Is the most accurate known.
In & given time. say III hour, "A pendulum will
make L number of oscillations dependent upon
the force OF gravity Il the place where it Is
swung. This force y4rIes with = chinge Of po-
sitiou OIL the earth, first, bectase tbs 'lstInce
from the center OK tie earth varies; : II, be-
cause the centrifugal force near the ( iat'f Ill
uInisheS the attraction oi the earth iEore than
it does as you approach the pole, where
the motion is less rapid. The centrifugal force Is
known 1t any place, and the relative force oil
gravity at different places may be found by COM
pairing the number OF oscillations OF the same
ndulum in a given length OF time at those
From the relative force of gravity at
tfyR places may be directly obtained their re-
~spective distances from the center of the earth,
Of course in a method requiring great accuracy
corrections have to be made for any slight yaria-
ton in the conditions under which he obserVa-
tons are taken, for instance the temperature Is
FREQUENTLY observed by inely-cOnstructed Their
mometers and the barometer Is also frequently
observed for variations Of temperature end
density. The pendulum is q hollow cylinder Of
brass about four feet long, one end OF which Is
loaded with lead 1t swings on one OF two steel
knife edges, which are symmetrcaily placed
near each end; the knife edge rests Oh Il polished
steel plate so that there is very little friction
~ 1,t-u, .-+,rfa a,riu.ttg Iy the hand
through an arc of about two degrees, and its own
momentum keeps it swinging when the heavy
end is down for almost live hours, while with
the heavy end up it swings only one third as
long. BY reversing the pendulum the resist
ance to the air is practically eliminated; having
once started the pendulum it is necessary to find
the time of Its starting, the end Of its SWING and
the number of oscillations made during shat
time. This time is actually determined by OBJ
seryatious of stars made with a portable transit
instrument. They are enabled to measure the
time with great accuracy by means of a chrome
.raph which consists essentially OF a revolving
cylinder, driven and regulated by appropriate
nachinery-on the cylinder is secured a sheet OF
paper, a little carriage bearing a pen makes 4 con-
tinuous spiral line on this sheet from one end to
the other of the cylinder. This pen is held by a
lever which every second is slightly moved by
An ordinary electro-maguet, thus recording on
the paper every second except the slxtleth'
which is omitted to indicate the beginning OF "A
minute. By means of an ordinary telegraph key
the circuit may be broken at will by the observer
thus recording any time which he may wish
for instance the transit of ii star across the
threads Of the transit instrument or the begin
ming of the pendulum swing; by means OF a scale,
the time NAV be measured from this record to thu
bundredth part of a second.
Instructions were sent from Washington to
the present observing party to visit Lahaina be-
cause previous observations had been taken
there in 1919 by the French under Mr.. Frey
cinet, Lahaina then being the principal town on
these islands. Messrs. Preston aud Brown sue
ceeded through the assistance of Mr.. Bishop, IN
finding the exact location of the previous sta
ton. The observations in Honolulu will end on
Friday night, aud We believe successfully on ae-
count of the uniform temperature that Is found
here.
Meesrs. Preston aud Brown speak of the uni
form kindness that was shown to them on these
islands. especially 10y HIS Excellency Gov
ernor DominIs and Professor Alexander, and we
beg to express to both, Mr.. Preston and Dir.
Brown, our appreciation OF their courtesy III
explaining all matters concerned with their re-