In admitting that I am going to promulgate a speculative hypothesis, that is a hypothesis for which there is evidence but not yet conclusive evidence, I must not lead you to suppose that the whole of what I have to say is of this character. On the contrary, much of it is certain, that is to say, is accepted by a consensus of opinion to-day among those who by reason of study are competent to judge. I will endeavor carefully to discriminate between what is in this sense certain and what must still be regarded as doubtful and needing further support.
To treat the subject properly, to give all the evidence as well as the results, would need a volume, or a course of lectures; and in order to be brief I must frequently be dogmatic, but I shall only intend to be so in those places where I feel sure that the physicists present (whom here I salute) will agree with me. When I have a dogma of this kind to propound I shall call it a thesis. The more speculative opinions I shall plainly denominate hypotheses.
1. My first thesis is that an electric charge possesses the most fundamental and characteristic property of matter, viz., mass or inertia; so that if any one were to speak of a milligram or an ounce or a ton of electricity, though he would certainly be speaking inconveniently, he might not necessarily be speaking erroneously. At the same time it would be well to mistrust any one who employed such a phrase, except in speaking to experts: he would most likely be talking nonsense; but if he talks nonsense to experts, his blood is on his own head.
In order to have any appreciable mass, however, an electric charge must either be extremely great or must be extremely concentrated; and, unless it is to be utterly masked by the matter with which it is associated, it must be the latter: that is to say, it must exist on bodies of far less than ultra-microscopic size. The mass or inertia of a charge depends upon two factors—the quantity of electricity in it, and its potential—and by concentrating a given charge on to a sufficiently small sphere, the latter factor can be raised theoretically to any value we please, and thus any required inertia can be obtained; unless a stage is reached at which it becomes physically impossible to concentrate it any more.
2. The next thesis is a very simple and familiar one, and dates virtually from the time of Faraday, though the conception has gradually gained in clearness and solidity: it is that every atom of matter can have associated with it a certain definite quantity of electricity called the ionic charge, that some atoms can have double this quantity, some treble, and so on, but that no atom or any piece of matter can have a fraction of this quantity, which therefore appears to be an ultimate unit, a sort of 'atom,' of electricity. The ratio of the charge to the weight of a material atom is measured with accuracy in electrolysis.
