He did not succeed in making the wire or the magnet revolve on its own axis.

The first great fact to be noticed is that the planets revolve around the sun in the same direction.

It followed that when the gun was elevated or depressed, the rack caused the pinion to revolve, and the sight was thus raised or lowered to the proper height to fulfil the conditions given above; but, as Colonel Watkin said, owing to want of level of platform and other causes it was not satisfactory.

Again, any plane w is the locus of a system of null-lines meeting in a point, called the null-point of c. If a plane revolve about a fixed straight line p in it, its ntill-point describes another straight line p, which is called the conjugate line of p. We have seen that the wrench may be replaced by two forces, one of which may act in any arbitrary line p. It is now evident that the second force must act in the conjugate line p, since every line meeting p, p is a null-line.

This consists of a cast-iron pan having a shallow cylindrical bottom holding mercury, in which a wooden muller, nearly of the same shape as the inside of the pan, and armed below with several projecting blades, is made to revolve by gearing wheels.