290 POPULAR SCIENCE MONTHLY. 



In admitting that I am going to promulgate a speculative hypoth- 

 esis, that is a hypothesis for which there is evidence but not yet con- 

 clusive 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 cer- 

 tain 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 fun- 

 damental 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 non- 

 sense ; 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 suflB- 

 ciently 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 grad- 

 ually 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 ulti- 

 mate 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. 



