150 THE HENRY. 



suininer of ^SlV2. Ho at once took up the subject, and by the aid of his 

 powerful apparatus was enabled to ])roduce striking verifications and 

 extensions of Faraday's conclusions. A description of tliese experi- 

 ments was published in Silliman's American Journal of Science for 

 July, 1832, and the article contains the first announcement of a most 

 important discovery, in whicli he anticipated Faraday by several years- 

 "Ik Marvel" wrote a sentence in Dream Life, wliich has been an 

 inspiration to many a young man, "There is no genius in life like the 

 genius of energy and industry;" and if the genius is to develop in the 

 direction of experimental science he might well have added, "and the 

 genius of attention to apparently unimportant, accidental phenomena." 

 It was this trait that was so highly developed in his character, this 

 anxi(ms solicitude that nothing, however trivial it might at the time 

 seem, should escape without note, that brought to Henry the honor of 

 the discovery of self-induction. 



Faraday had found that when a current of electricity through one cir- 

 cuit was started, or stopped, or altered in strength, a current would be 

 induced in a neighboring circuit; but the induction of apart of the cir- 

 cuit upon another part, or self-induction, ha<l escaped him. Henry saw 

 it in the interesting and previously unobserved fact that if the poles of 

 a l)attery of no very great i)ower be connected by a long wire, and the 

 circuit be suddenly broken, a spark will be produced at the point of 

 interruption, while if the connecting wire be short a spark will not be 

 ])roduc'ed. He also noted that the eftect was increased by coiling the 

 ^vire into a helix, and he remarked, at the close of the article describ- 

 ing these experiments, "lean account for these phenomena only by 

 supposing the long wnre to become charged with electricity, which, by 

 its reaction on itself, projects a spark when the connection is broken."' 

 This was a capital observation; but, although published in 1832, it 

 Avas apparently unknown to Faraday, who rediscovered the fact a lew 

 years later and announced it as new. As a matter of fact, it appears 

 that Faraday did not himself observe the fundanu^ntal phenomenon, 

 but that his attention was called to it by a friend. His announcement 

 was made in the Philosophical Magazine in 1834, and in a communi- 

 cation to the Iloyal Society in 1835 he extended and enlarged upon the 

 observation. 



In much that he had done, however, he had been anticipated by 

 Henry, who, although greatly interrupted in his original investigations 

 by his removal from Albany to Princeton, had himself taken up the 

 phenomenon of self-induction and made an interesting research. 



As time and opportunity allowed, Henry continued his electrical inves- 

 tigations during the years that followed. He was the first to obtain 

 induction from induced currents, and he made a classic investigation of 



' There is good reason for believiiis tliat Heury had observed tliis pheuoiiienoii at. a 

 much earlier date than that of publication, and that the observation was really 

 made before the discovery of induction by Faraday. 



