FARADAY. 789 



tracing the subsequent history of his discovery. As might be expected, it was 

 at once made the subject of investigation by the whole scientific world, but 

 some of the most experienced physicists were unable to avoid mistakes in 

 stating, in what they conceived to be more scientific language than Faraday's, 

 the phenomena before them. Up to the present time the mathematicians who 

 have rejected Faraday's method of stating his law as unworthy of the preci- 

 sion of their science have never succeeded in devising any essentially different 

 formula which shall fully express the phenomena without introducing hypotheses 

 about the mutual action of things which have no physical existence, such as 

 elements of currents which flow out of nothing, then along a wire, and finally 

 sink into nothing again. 



After nearly half a century of labour of this kind, we may say that, 

 though the practical applications of Faraday's discovery have increased and are 

 increasing in number and value every year, no exception to the statement of 

 these laws as given by Faraday has been discovered, no new law has been 

 added to them, and Faraday's original statement remains to this day the only 

 one which asserts no more than can be verified by experiment, and the only 

 one by which the theory of the phenomena can be expressed in a manner 

 which is exactly and numerically accurate, and at the same time within the 

 range of elementary methods of exposition. 



During his first period of discovery, besides the induction of electric cur- 

 rents, Faraday established the identity of the electrification produced in different 

 ways ; the law of the definite electrolytic action of the current ; and the fact, upon 

 which he laid great stress, that every unit of positive electrification is related in 

 a definite manner to a unit of negative electrification, so that it is impossible 

 to produce what Faraday called "an absolute charge of electricity" of one 

 kind not related to an equal charge of the opposite kind. 



He also discovered the difference of the capacities of different substances 

 for taking part in electric induction, a fact which has only in recent years 

 been admitted by continental electricians. It appears, however, from hitherto 

 unpublished papers that Henry Cavendish had before 1773 not only disco- 

 vered that glass, wax, rosin and shellac have higher specific inductive capacities 

 than air, but had actually determined the numerical ratios of these capacities. 

 This, of course, was unknown both to Faraday and to all other electricians of 



his time. 



The first period of Faraday's electrical discoveries lasted 10 years. In 1841 he 



