Polarity. The two ends of a magnet behave in exactly opposite ways with regard to other magnets and electric currents, and on this account a, magnet is said to possess polarity; it has two poles endowed with opposite properties. This is not to be explained by supposing the two ends magnetised with different kinds of magnetism, for such is not the fact; the nature of magnetism is essentially rotary, and all rotating bodies possess a kind of polarity. Suppose two cylinders, A B and C D, to be rotating on their axes in the same direction, the ends B and c are, of course, turning in the same direction as shown in the upper figure; but if, without changing the direction o its rotation we now turn c D about a line E F so as to bring it into the position shown in the lower figure, the ends b and D are turning in opposite directions. Now these two cylinders may be considered roughly analogous to two magnets, if we substitute a whirl of electricity for the actual rotation of the cylinders; then A and c would be, say, north poles, and B and D south poles. This two-endedness, or polarity, is characteristic of rotating bodies; a revolving shaft appears to be turning either right-handedly or left-handedly as we view it from one end or the other. A coil of wire carrying a current behaves, of course, just like a magnet, and similarly has polarity.