Again we do not stop at this bare inference. By another sense, that of pain, or mere sensation, we discriminate between masses of matter in apparently intimate relation with ourselves, and other or foreign lumps of matter; and we use the first portion as a measure of the extent of the second. The human body is our standard of size. We proceed also to subdivide our idea of matter,--according to the varieties of resistance with which it appeals to our muscular sense,--into four different states, or "elements" as the ancients called them; viz. the solid, the liquid, the gaseous, and the etherial. The resistance experienced when we encounter one or other of these forms of material existence varies from something very impressive--the solid,--through something nearly impalpable--the gaseous,--up to something entirely imaginative, fanciful, or inferential, viz. the ether. The ether does not in any way affect our sense of touch (i.e. of force); it does not resist motion in the slightest degree. Not only can our bodies move through it, but much larger bodies, planets and comets, can rush through it at what we are pleased to call a prodigious speed (being far greater than that of an athlete) without showing the least sign of friction. I myself, indeed, have designed and carried out a series of delicate experiments to see whether a whirling mass of iron could to the smallest extent grip the ether and carry it round, with so much as a thousandth part of its own velocity. These shall be described further on, but meanwhile the result arrived at is distinct. The answer is, no; I cannot find a trace of mechanical connection between matter and ether, of the kind known as viscosity or friction.