Crowds are said to flock daily to the Panthéon to witness this interesting experiment. It has been successfully repeated at the Russell Institution, and preparations are being made in some private 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° per hour. Explanations, however, will be necessary from lecturers and others who give imitations 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 understood 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 representative 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 Panthéon elucidation constitutes its sole application. By it the latitude maybe 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 suspended 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 again descend, and so oscillate forward and backward 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."