But since each class of Polar Phenomena is thus referred to an ulterior cause, of which we know no more than that it has a polar character, it follows that _different_ Polarities may result from the _same_ cause manifesting its polar character under different aspects. Taking, for example, the hypothesis of globular particles, if electricity result from an action dependent upon the _poles_ of each globule, magnetism may depend upon an action in the _equator_ of each globule; or taking the supposition of transverse vibrations, if polarized light result directly from such _vibrations_, crystallization may have reference to the _axes_ of the elasticity of the _medium_ by which the vibrations are rendered transverse,--so far as the polar character only of the phenomena is to be accounted for. I say this _may_ be so, _in so far_ only as the polar character of the phenomena is concerned; for whether the relation of {372} electricity to magnetism, or of crystalline forces to light, can really be explained by such hypotheses, remains to be determined by the facts themselves. But since the first necessary feature of the hypothesis is, that it shall give polarity, and since an hypothesis which does this, may, by its mathematical relations, give polarities of different kinds and in different directions, any two co-existent kinds of polarity may result from the same cause, manifesting itself in various manners. The conclusion to which we are led by these general considerations is, that two co-existing classes of polar phenomena _may_ be effects of the same cause. But those who have studied such phenomena more deeply and attentively have, in most or in all cases, arrived at the conviction that the various kinds of Polarity in such cases _must_ be connected and fundamentally identical. As this conviction has exercised a great influence, both upon the discoveries of new facts and upon the theoretical speculations of modern philosophers, and has been put forward by some writers as a universal principle of science, I will consider some of the cases in which it has been thus applied.