Western union. (City of Hannibal, Mo.) 1850-1851, 1851-05-08
Tho Rotation Of the Earth Rendered
Visible.

The experiment now being exhibited in Par
is, by which the dinrnal rotation of the earth,
is rendered palpable to the senses, 10 certainly
one Of the most remarkable Of the modern yer.
iiicatious of theory. AT attached, from which
sphere Of metal, four or five inches in diam
eier, is suspended SO as to hang near the floor
of the building. This apparatus is put in vibrs.
ton after the manner If pendulum. Under
and concentrica with it, is plsced a circular Ia.
Gle, some twenty feet in diameter, the circum.
ference of which is divided into degrees, min
utes, Sc and the divisions numbered. Now,
it can be shown by the most elementary prin-
cples of mechanics, that supposng the earth
to have the diurna motion upon its axis which
is imputed 10 it, aud which explains the phe-
nomena of day and night, &c., the plane in
which this pendulum vibrates will not be CLEO.
ted by this diurnal motion, but will maintain
strictly the same direction during "a hours
In this interval, however the table over which
the pendulum is suspended will continually
change its position, in virtue of the diurnal mo.
ton, so as to make a complete revolution round
its centre. Since then, the table thus revolves,
and the pendulum which vbrates over it does
not revolve, the consequence is, that limo
traced upon the table by point projecting from
the bottom of the ball, will change its direction
relatively to !he table from minute to minute,
and from hour to hour, so that il such point were
pencil and that paper spread upon the table,
the course formed by this pencil during "a hours,
would form system OF lines radiating from the
centre of the table, and the two lines formed
after the interval of one hour, would always
form angle with each other of Is deg, being
, the 2lth part Of the circumference.
Now, this is rendered actually visible to the
crowds which daily flock to the Pantheon 10
i witness this rpmark blp eyrnyi,pcpf Tho
= pracised eye of correct observer, especially
If aided by proper optical instrument, may
actually the motion which the table has in
common with the earth under the pendulum.
between two successive vibrations. 1t 10, in
fact, apparent that the ball, or rather the point
attacheh 10 the bottom of the ball, does not re-
turn precisely Ia the same point Of the circum-
ference Of the table after two successive vibra-
tons. This is rendered visible tho motion
" which the table has in common with the earth.
. 1t is true that correctly speaking, the table does
not turn round by its centre, but turns round
u the axis Of the earth ne, erheess the effect OF
u the motion relatively 10 the pendulum suspen-
" died over TIE centre of the table is precisely the
- same as il would be if the table moved once in
twenty four hours round its own centre, for
although the table be turned in common with
u the surface of the earth round the earths axis
. the point OF suspension ii the pendulum il
10 turned also in the same time round the same
4 axis, being continually maintained vertical above
the centre of the table. The plane in which
III the pendulum vibrae does not, however, par
? take of this motion, and consequently has tn.
!" appearance OF revolving once in twenty -four
re hours the table, while, in reality it is tn,
10 table which revolves once in twenty four hour
10 under it.