THE HENRY. 15 1 



mutual inductiou aud of curreuts of the secoud, third, fourth, and 

 higher orders. lu addition to Ids discovery of self-induction, his 

 researches on the inductive ettects of transient currents, on magnetic 

 screening', and especially on the oscillations ot the electric discharge 

 were on new lines and of the highest order. The investigation of the 

 oscdlations of an electric discharge, one of the most important of all, 

 was almost unrecognized until nearly a half century had elapsed. It 

 was published in the Proceedings of the American Philosophical Soci- 

 ety in 1842. In it he says: "The phenomena require us to admit the 

 existence of a principal discharge in one direction, and then several 

 reflex actions, backward and forward, each more feeble than the pre- 

 ceding, until the equilibrium is obtained." 



Two years later ITelmholtz wrote: "We assume that the discharge is 

 not a simple motion of the electricity in one direction, but a backward 

 and forward motion between the coatings, in oscillation, which become 

 continually smaller, until the entire vis viva is destroyed by the sum 

 of the resistances;" and in 1853 Prof. W.Thompson published in the 

 Philosophical Magazine a mathemati(!al investigation of Transient 

 Electric Currents, developing an equation in which " the whole theory 

 is packed up." 



Concerning the influence of Henry's discoveries on the marvelous 

 Ijrogress of electricity during the past five or ten years, it may be well 

 to rest upon the opinion of one of England's leading electricians, who, 

 in the preface to a recent volume on one of the latest i)hases of electri- 

 cal development, writes as follows: 



"At the head of this long line of illustrious investigators stand pre- 

 eminent the names of Faraday and Henry. On the foundation stones 

 of truth laid down by them all subse(|uent builders have been content 

 to rest. The experimental researches of the one have been the guide 

 of the experimentalist no less than the instructor of the student, since 

 their orderly and detailed statements, alike of triumphant discovery 

 and of suggestive failure, make them independent of any commentator. 

 The scientific writings of Henry deserve hardly less careful study, for 

 in them we have not only the lucid explanations of the discoverer, but 

 the suggestions and ideas of a most profouiul aud inventive mind, and 

 which indicate that Henry had early touched levels of discovery oidy 

 just recently becoming fully worked." ' 



That one whose work is so highly esteemed should have been selected 

 for honor in the international chamber of delegates is not surprising. 

 It was also eminently fitting that his name should be given to the unit 

 of induction. 



As already intimated, the strength of the induced current depends 

 on the rapidity with which that of the inducing current is altered. 

 The sudden stopj)ing of a current must be regarded as decrease at a 

 very rapid rate, and the starting of a current as increase at a rapid 



'Fleniiug. The Alternate Current Transformer in Theory and Practice, Vol. I, 

 London, 1889. 



