"It is perfectly absurd for persons unacquainted with mechanical and geometrical science to presume to make the experiment. Indeed, such efforts deserve rather the name of conjuring than of experiment; but in this, as in many other matters of life, it is true that "fools rush in where angels fear to tread." Perhaps the too hasty rush at the experimental verification of Foucault's law may account for some persons in England, whose opinions when given with due deliberation are entitled to respect, having allowed themselves to express doubts (which I understand, however, have been since retracted) as to the truth of the law itself. In Paris there was no difference of opinion among such men as Lamé, Poinsol, Binet, Leonville, Sturm, Chasles, Bruvues, I believe Arago, Hermite, and many others with whom I conversed on the subject, except as to the best mode of making the theory popularly intelligible." Explanations 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 silkworm'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. Doubtless we shall soon have public exhibitions of the demonstration in all our cities. 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 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 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 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." [Illustration] THE BUTCHERS' LEAP AT MUNICH.