Recent Theories of Electricity. 209 



The Zeeman effect, in its elementary form* is satisfactorily 

 explained by this theory, although the recently discovered 

 complex character of the phenomenon is not accounted for. 



Radioactivity, on the whole, is best explained by the 

 projection of positive and negative electrons from a certain 

 class of bodies. 



And lastly, Kaufmann has shown by a delicate experiment 

 that the effective inertia of an electron is a function of its 

 velocity. This conclusion has been confirmed by others, 

 although in minor points there is a considerable difference in 

 results and opinions. 



It must not be lost sight of that all these experiments 

 deal with quantities of matter, supposing it to exist, too small 

 to be appreciable by either chemical analysis or mechanical 

 apparatus, such as the balance, etc. They are ultimately 

 measured by the force of electrical attraction of an electrical 

 charge. We are, therefore, experimenting with matter which 

 appeals to us through only one of its attributes. Is it not 

 almost inevitable that an exclusive attention paid to this 

 single attribute is likely to exalt it into an undue prominence ? 

 We have had, in the past, examples of much the same sort o£ 

 reasoning. When the phenomena of light were predominantly 

 discussed, physicists drifted into the opinion that this property 

 of matter could be explained only by creating a light sub- 

 stance. Again, this process of reasoning occurred when beat 

 was first investigated : we had the creation of caloric. And 

 now we are asked to do the same thing with electricity. It 

 is safe to predict that history will be repeated again, and that 

 electrical charges and their forces will also sink into the 

 condition of an attribute of matter. 



It might certainly be true that two experiments showing- 

 equal electrical charges would, if we could measure the 

 amount of matter concerned, provide us with unequal quan- 

 tities of matter, just as conversely equal quantities of matter 

 might show different quantities of electricity. The hypothesis 

 of equivalence of electrical charge and matter rests solely on 

 an analogy to electrolysis, where matter is in a quite different 

 state and also where the equivalence may be only approximate. 

 Matter, on the other hand, in a solid state shows no connexion 

 between volume and density and electrical charge. In dealing 

 with electricity we should not forget the immense superiority 

 of electrical detectors in delicacy to those for mechanical 

 quantities, so that w T e can appreciate far smaller quantities of 

 electrified than of neutral bodies. 



There is no doubt, from the quotations given, that theorists 

 are basing their work on the assumption of the electron as the 



Phil i%. S. 6. Vol. 21. No. 122. Feb. 1911. P 



