pendulum hung from a steel plate in such a manner as to move freely in any vertical plane. To start the oscillatory movement without giving the ball any bias, it was drawn to one side with a cord, which held the ball by a loop; the cord was then burned, after which the loop fell off, and the vibrations (generally limited to an arc of 15 or 20 degrees) commenced. In one minute the ball had sensibly deviated from the original plane of vibration towards the observer’s left. Afterwards he experimented at the Observatory with a pendulum 11 metres (30 feet) long, and latterly at the Pantheon with one still longer. The advantage of a large pendulum, as compared with a small one, is, that a longer time elapses before it comes to a state of rest; for machinery cannot be employed here, as in a clock, to continue the motion. The pendulum is suspended over the centre of a circular table, whose circumference is divided into degrees and minutes. The vibrations are begun in the manner above described, and in a short time it is observed that the pendulum, instead of returning to the same point of the circle from which it started, has shifted to the left. If narrowly observed, the change in the plane of vibration (says M. Foucault) is perceptible in one minute, and in half an hour, “Il saute aux yeux,” it is quite palpable. At Paris the change exceeds 11 degrees in an hour. Thus, supposing the oscillations to commence in a plane directed south and north, in two hours the oscillations will point SSW. and NNE.; in four hours they will point SW. and NE.; and in eight hours the oscillations will point due east and west, or at right angles to their original direction. To a spectator the change seems to be in the pendulum, which, without any visible cause, has shifted round a quarter of a circle; but the real change is in the table, which, resting on the Earth, and accompanying it in its rotation, has performed a fourth (and something more) of its diurnal revolution. No one anticipated such a result; and the experiment has been received by some with incredulity, by all with wonderment; and one source of the incredulity arises from the difficulty of conceiving how, amidst the ten thousand experiments of which the pendulum has been the subject, so remarkable a fact could have escaped notice so long. Fully admitting that these experiments have generally been conducted with pendulums which had little freedom of motion horizontally, we still think odd that somebody did not stumble upon the curious fact.