Supposing an atom thus broken up into electrons, its weight may possibly have disappeared. We simply do not know whether weight is a property of the grouping called an atom, or whether it belongs also to the individual ingredients or corpuscles of that atom. There is at present no evidence. But whether weight has disappeared or not, it is quite certain, for definite though rather recondite theoretical reasons, that the inertia would _not_ have disappeared; and accordingly it may be held, and must be held in our present state of knowledge, that the constancy of fundamental material still holds good, even though the atoms are resolved into electric charges—an amount of destruction never contemplated by those chemists and physicists who promulgated the doctrine of the conservation of matter. _Electrical Theory of Matter._ But then, on the electrical theory of matter, even _inertia_ is not the thoroughly constant property we once thought it. It is a function of velocity for one thing, and when speeds become excessive the inertia of matter rises perceptibly in value. The fact that it would rise in value by a calculable amount, and that the rise would be perceptible when the speed of motion approached in value to within, say, a tenth of the velocity of light, was predicted mathematically;[1] and now, strange to say, it has recently become possible to observe and actually measure the increase of inertia experimentally, and thus to confirm the electrical theory not only as qualitatively or approximately true, but as completely and quantitatively accurate. A remarkable achievement all this! of quite modern times, which has not excited the attention it deserves—save among physicists. [Footnote 1: By Mr Oliver Heaviside and Professor J. J. Thomson.]