NEW PROOF OF THE EA_RTII'S ROTATION.
THE earth does move notwithstanding," whispered Galileo, leav- ing the dungeon of the Inquisition : by which he meant his friends to understand, that if the earth did move, the fact would remain so in spite of his punishment. But a less or- thodox assembly than the conclave of Cardinals might have been staggered by the novelty of the new philosophy. Ac- cording to Laplace, the apparent diurnal pheenomena of the heavens would be the same either from the revolution of the sun or the earth ; and more than one reason made strongly in favour of the prevalent opinion that the earth, not the sun, was stationary. First, it was most agreeable to the impression of the senses ; and next, to disbelieve in the fixity of the solid globe, was not only to eject from its pride of place our little planet, but to disturb the long-cherished sentiment that we ourselves are the centre—the be-all and end-all of the universe. However, the truth will out ; and this is its great distinction from error, that while every new discovery adds to its strength, falsehood is weak- ened and at last driven from the field.
That the earth revolves round the sun, and rotates on it's polar axis, have long been the settled canons of our system. But the rotation of the earth has been rendered visible by a practioal de- monstration, which has drawn much attention in Paris, and is be- ginning to excite interest in this country. The inventor is M. Foucault; and the following description has been given of the mode of proof. "At the centre of the dome of the Pantheon a fine wire is attached, from which a sphere of metal, four or five inches in diameter, is suspended so as to hang near the floor of the building. This apparatus is put in vibration after the manner of a pendulum. Under and concentrical with it, is placed a circular table, some twenty feet in diameter, the circumference of which is divided into degrees, minutes, &e., and the divisions numbered. Now, supposing the earth to have the diurnal motion imputed to it, and which explains the phamomena of day and night, the plane in which this
dulum vibrates will not be affected by this motion, but the table over w
the pendulum is suspended will continually change its position in virtue of the diurnal motion, so as to make a complete revolution round its centre. Since, then, the table thus revolves, and the pendulum which vibrates over it does not revolve, the consequence is, that a line traced upon the table by a 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 a pencil and that paper were spread upon the table, the course formed by this pencil would form a system of lines radiating from the centre of the table. The practised eye of a 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 successive vibrations. It is, in fact, apparent that the ball, or rather the point attached to the bottom of the ball, does not return precisely to the same point of the circumference of the table after two successive vibrations. Thus is rendered visible the motion which the table has in common with the earth."
Crowds are said to flock daily to the Pantheon to witness this interesting experiment. It has been successfully repeated at the Russell Institution, and preparations are being made in some pri- vate houses for the purpose. A lofty staircase or room twelve or fourteen feet high would suffice ; but the dome of St. Paul's, or, as suggested by Mr. Sylvestre in the Times, the transept of the Crystal Palace, offers the most eligible site. • The table would make its revolution at the rate of 15° pet hour. Explanations, however, will be necessary from lecturers and others who give imi- tations of M. Foucault's ingenuity, to render it intelligible to those unacquainted with mathematics, or with the laws of gravity and spherical motion. For instance, it will not be readily under- stood by every one why the pendulum should vibrate in the same plane, and not partake of the earth's rotation in common with the table ; but this could be shown with a bullet suspended by a silk- worm's thread. Next, the apparent horizontal revolution of the table round its centre will be incomprehensible to many, as repre- sentative of its own and the earth's motion round its axis. Perhaps Mr. Wyld's colossal globe will afford opportunities for simplifying these perplexities to the unlearned.
The pendulum is indeed an extraordinary instrument, and has been a useful handmaid to science. We are familiar with it as the time-regulator of our clocks, and the ease with which they may be made to go faster or slower by adjusting its length. But neither this nor the Pantheon elucidation constitutes its sole application. By it the latitude may be approximately ascertained, the density of the earth's strata in different places, and its elliptical eccentricity of figure. The noble Florentine already quoted was its inventor; and it is related of Galileo, while a boy, that he was the first to observe how the height of the vaulted roof of a church might be measured by the times of the vibration of the chandeliers sus- pended at different altitudes. Were the earth perforated from London to our antipodes, and the air exhausted, a ball dropped through would at the centre acquire a velocity sufficient to carry it to the opposite side, whence it would agein descend, and so oscillate forward and backwards from one side of the globe's surface to the other in the manner of a pendulum. Very likely, the Cardinals of the Vatican would deem this heresy, or "flat blasphemy."
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