Green-Mountain freeman. [volume] (Montpelier, Vt.) 1844-1884, 1851-07-17
For the freeman
Rotation of the Earth.

ISOCdC4On OF Cho EafCn.
MR.. EDITOR Passing through Charleston,
few days since, was led by curiosity to call
at Bunker Hill Monument and see the operation
of the pendulum, SO much talked of. While
there, Prof. HosFoRD, of Cambridge, who erect
ed the pendulum, came in for the purpose of try
ing experiments. By his invitation went in 10
witness and assist in performing the experiments
thus having favorable opportunity to observe
and learn. The result of these observations may
be of some interest to your readers. The pen
dulum is suspended within the monument, by a
small steel wire two hundred and seventeen feet
in length, fastened at the top, and also to the
pendulum, by clamp screw consequently its
construction can give it no tendency to oscillate
u clie direc Ion Biore feaGily than H. a,
change its direction when in motion, or oppose
any obstacle to change, if acted on by any
other force. When first set in motion it oscil-
lates about four feet, and having no other force
to act upon it, it continues in motion but six
hours; each oscillation occupying eight and one
sixteenth seconds. Beneath it is graduated
disc. The result of several experiments shows
that it varies to the east one degree in about
five minutes and fifty-sx seconds; and would
perform an entire revolution on the disc, in thr-
ty-fve hours and thirty-six minutes. II further
experiments show these to be correct, it will prove
that in one point at least, the theory is estab-
lished by facts. The theory usually advanced
is based wholly upon the following fact or as
sumption, viz: that pendulum once set in
motion will continue to vibrate in the same or
parallel direction. To illustrate: suppose one
suspended over either pole; if it continued to
oscillate In the same direction, without regard
to the position of the earth, it will in twenty
four hours cut every point in the horizon. To
illustrate its motion at any other point, take an
orange and mark on it the equator, tropics and
a few of the parallels and merdans; also pre-
: pare several plates of tin one and half inches
: wide by two in length. Suppose a pendulum
: in motion due north and south, the southern
point of its oscillation being the tropic of Cap
ricorn Insert upon any given meridian q
; plate of tin, reaching from the troplc to the
5 North pole. This will represent the extended
plane of the first oscillation. Then pass twenty
degrees east upon the tropic and insert the Sec
ond plate parallel teah the first. Instead of
a touching the north pole it will bear several de-
gress to the east. This will represent the plane
/ of the pendulum's oscillation three hours after
q it is set in motion, or when the earth has per-
: formed one eighth of revolution. Others may
: also be inserted, showing the continued varia-
: tion Again, suppose the pendulum set in mo-
e Etion due eat and west. Mark distinct line
: longtudinaily across the centre OF the plates
Place the plate, for instance, upon the slxtleth
= parallel of north latitude the centre line being
e upon the parallel,) at right angles with the me
ridans, and insert it to the centre Of the orange
n This represents the plane of oscillation, ant
Z does not correspond with the plane of the paral
lei, since it will be seen that while the centre il
o in sixty degrees north latitude, at the surface
st the edges are both south of that and the entire
= plane extending from the surface to the centre
q huSlC VIII plduC vi pulul
lei. Pass twenty degrees east of this and in
NJ sert another plate, the centre falling upon the
ID same line with the centre of the first and tn
'e whole plate parallel with it. This will represen
OF the plane of oscillation three hours after set il
OF motion, or after the earth has passed through
Id twenty degrees of its diurnal revolution. In
Mt stead of both edges being south Of sixty de
IN grees, half of the plane will bear considerabl
le to the north, and the other to the south. Trl
III the same experiment at the equator, and thert
IL will be no variation. 1t will thus be seen tina
OF wherever the pendulum be placed the equatC
r. excepted) or in whatever direction it be set
1y motion, there is constant variation in the sam
ne direction, which variation increases or diminish
E. es in proportion as the meridians are more c
MS less convergent. The pendulum has severt
he other motions, some OF which are not yet salts
factory accounted for. Its position vare
slightly when in a state of rest in consequence
of the expansion of the different sides of tn
ne monument by the heat of the sun. When frs
- set in motion, it appears to pass back and fort
IL in the same lice, but in the course of ten min
IL utes 1t can plainly be perceived that it describe
lg an ellipse, which increases in breadth with tn
as shortness of the stroke. This pendulum ha
s. now been in operation for several weeks, an
IL Prof. Hosford is engaged in experimenting an
K collecting facts, which hereafter may prove G
IL great value.
a July THos. P. HATCH.