American telegraph. [volume] (Washington [D.C.]) 1851-1851, 1851-05-22
MOTION OF THE EARTH AND PENDU
LUMS

TO the Editors Of the american Telegraph.
GENTLEMEN: Having amused myself during
few moments of leisure, rejecting on the
aforementioned subject, l thought it might
serve to entertain some Of your numerous read
ers, were place given to the results in your
interesting paper, and therefore communicate
them for that purpose, or to be passed quietly
under the editorial table, into the Office trash
bag, as you may deem most advisable.
l. If pendulum, in state of rest, be car
ried horizontally and steadily with any velocity,
the bob by its vis inertia "a well-known property
of bodies) will fall, or lag, behind the dead
point which means the point where the pendu-
lum would naturally be at rest if let alone.
2. If a pendulum, with an iron or steel bob,
be set in vibration in any given direction, and
magnet drought near enough to influence it)
be presented towards it in direction ut right
angles to the line of vibration, and directly OPP
posite the dead-point, the general direction of
the vibrations will remain unchanged; but if
the magnet be removed ever SO little to one side
of the dead-point, the directions Of the vibra-
tons will be changed continually at each vibra-
ton, until the bob will finally strike the magnet.
If the magnet, however, could be constantly
kept in the same relative position to the direc-
ton of the successive vibrations, by moving it
with uniform velocity in circle, with the dead
point as a centre, the pendulum, during its
vibrations, would also revolve in a circle.
The above facts, which any one can establish
to his own satisfaction by experiment, are suffi-
cient to explain the so much talked-of new dis
covery of the revolution of the pendulum caused
by the motion Of the earth, by simply taking in
connexion Herewith another fact, to wit, that
pendulum when at rest in any latitude tends
nearly to the centre of the earth, whilst the mo-
20
parallel of latitude) e1erts constant uniform
force in an oblique direction on the bob, pre-
cisely similar in its effects to the force of the
magnet in the above experiment when applied
to one side of the dead-point. Immediately on
the equator, however, where the bob of the
pendulum, the point Of suspension, and the
earth's centre, are oil in the same right line,
there will be no revolution, since the force ex-
erted by the earth's motion at that point is not
angular, but directly opposite the dead-point.
1t is singular coincidence also, that the velo-
city of the eafths surface diminishes directly
in proportion to the distance from the pole, and
the angle of inclination Of the pendulum rod to
the earth's axis diminishes in the same ratio !;
the effects of the disturbing force will therefore
be equalized, SO that the times of revolution Of
pendulums will be the same in all ATTITUDES,
only on opposite sides of the equator they will
reVolVc III contrary ulrectlonS.
Those who still doubt the effects above as
cribed to the earth's motion may satisfy them
selves of the truth, think, by the following
simple experiment: Suspend weight to o
string, and, when in a state of rest move the
point of suspension slowly around in small
circle, and the weight will Immediately begin to
revolye, and will continue as long as the motion
is kept up. Now assuming latitude very near
either pole of the earth, the point of suspension
of the pendulum, if permanently suspended
there, would be carried through q circle in a
similar manner, at the rate of one revolution in
twenty -four hours, producing similar but pro-
portionate results-the rod, be it borne in mind,
being at that point nearly parallel to the axis
of the earth; and if the pendulum be yibrated,
as the disturbing force acts nearly at right an
giles to the rod, the effect would be nearly the
same. If, after all, there be any who can resist
this evidence of their own senses, fear we
shall have to postpone their conversion until
some of our ingenious countrymen have placed
daily clocks on our parlor mantel-pieces, con-
structed on the above simple principle.