Green-Mountain freeman. [volume] (Montpelier, Vt.) 1844-1884, 1851-05-22
Rotation of the Earth Rendered
Visible.

The experiment now being exhibited in Paris,
by which the durnal rotation Of the earth is rem
dered palpable to the senses, is one of the most
remarkable Of the modern verfcatons of theo-
ry. Although the demonstration by which the
rotation of the earth has been estabishe be
such as to carry conviction to the minds Of all
who are capable Of comprehending it, to which
nothing can be imagined to add either force or
clearness, nevertheless even the natural phi loso-
pher himself caDnot regard the present expert
mcnt without feelings OF profound Interest und
satisfaction, and to the great mass, to whom the
complicated physical phenomena by which the
rotation of the earth has beer established ere
incomprehensble, this experiment is invalua-
Bile.
At the centre of the dome of the Pantheon
fine wire is attached, from which sphere of
metal, four or five inches IN diameter, is sus-
pended so as to hang near the floor Of the build
ing. This apparatus is put in vibration after
the manner of pendulum. Under, and con-
centrical with it, is placed circular table some
twenty feet in diameter, the circumference of
which is divided into degrees, minutes, &c., and
the divisions numbered. Now, it can be shown
by the most elementary principles of mechanics,
that supposing the earth to have the diurnal mo.
tion upon its axis which is imputed to it, and
which explains the phenomena of day and night,
&c, the plane in which this pendulum vibrates
will not be affected by this diurnal motion, but
will maintain strictly the same direction during
twenty-four hours. In this interval, however,
the table over which the pendulum is suspended
will continually change its position in virtue of
the dlurnal motion, SC as to make complete
revolution round its centre.
Since, then, the table thus revolves, and the
pendulum which vibrates over it does not re-
volve, the consequence is that line traced upon
the table by point projecting from the bottom
of the ball will change its direction relatively
to the table, from minute to minute and from
hour to hour, so that if such point were pen
Gil and that paper were spread upon the table,
the course formed by this pencil during twenty
four hours would form a system of lines radia-
ting from the centre of the table, and the two
lines formed after the interval Of one hour would
always form an angle with each other Of Is .,
being the 24th part of the circumference, Now
this is rendered actually visible to the crowds
which daily flock to the Pantheon to witness
this remarkable experiment The practised eye
of correct observer, especially if aided by a
proper optical instrument, may actually see the
motion which the table has in common with the
earth, under the pendulum, between two sue
cessive vibrations. It's, in fact, apparent that
the ball, or rather the point attached to the ball
does not return precisely to the same point Of
the circumference of the table after two sue
cessve vibrations, Thus is rendered visible
the motion which the table has in common with
the earth.
1t is true that, correctly speaking, the table
does not turn round its own centre but turns
round the axis of the earth nevertheless, the
effect of the motion relatively to the pendulum
suspended ever the centre of the table, is pre-
csely the same as it would be if the table NOV
ed once in twenty hours round its own
centre, for although the table be turned, in com
mon with the surface of the earth, round the
earth's axis, the point of suspension of the pen
dulum is turned also in the same time round the
same axis, being continually maintained yerti.
cal above the centre of the table, The plane
in which the pendulum vibrates does not, how
ever, partako of this motion, and, consequently
has the appearance of revolving once in twenty
four hours over the table, while, in reality, it is
the table which revoves ouce in twonty-four
hours under it,