418 Professor Oliver Lodge [March 8, 



experimentalist, Joseph Henry, of Washington, a man not wholly 

 unlike Faraday in his mode of work, though doubtless possessing to 

 a less degree that astonishing insight into intricate and obscure 

 phenomena ; wanting also in Faraday's circumstantial advantages. 



This great man arrived at a conviction that the Leyden jar dis- 

 charge was oscillatory by studying the singular phenomena attending 

 the magnetisation of steel needles by a Leyden jar discharge, first 

 observed in 18-4 by Savary. Fine needles, when taken out of the 

 magnetising helices, were found to be not always magnetised in the 

 right direction, and the subject is referred to in Germtin books as 

 anomalous magnetisation. It is not the magnetisation which is 

 anomalous, but the currents which have no simple direction ; and 

 we find in a memoir j^ublished by Henry in 1842, the following 

 words : — 



" This anomaly, which has remained so long unexplained, and 

 which, at first sight, appears at variance with all our theoretical ideas 

 of the connection of electricity and magnetism, was, after considerable 

 study, satisfactorily referred by the author to an action of the dis- 

 charge of the Leyden jar, which had never before been recognised. 

 The discharge, whatever may be its nature, is not correctly repre- 

 sented (employing for simplicity the theory of Franklin) by the 

 single transfer of an imponderable fluid from one side of the jar to 

 the other ; the phenomenon requires us to admit tlie existence of a 

 'principal discharge in one direction and then several reflex actions 

 hacliword and forward each more feeble than the preceding, until the 

 equilibrium is obtained. All the facts are shown to be in accordance 

 witli this hypothesis, and a ready explanation is afibrded by it of a 

 number of j^benomena, which are to be found in the older works on 

 electricity, but which have until this time remained unexplained."* 



The italics are Henry's. Now if this were an isolated passage it 

 might be nothing more than a lucky guess. But it is not. The 

 conclusion is one at which he arrives after a laborious repetition 

 and serious study of the facts, and he keejis the idea constantly 

 before him when once grasped, and uses it in all the rest of his 

 researches on the subject. The facts studied by Henry do in my 

 opinion sujiport his conclusion, and if I am right in this it follows 

 that he is the original discoverer of the oscillatory character of a 

 spark, although he does not attemj)t to state his theory. TLat was 

 first done, and comj^letely done, in 1853, by Sir William Thomson ; 

 and the progress of experiment by Feddersen, Helmholtz, Schiller, 

 and others has done nothing but substantiate it. 



The writings of Henry have been only quite recently collected 

 and published by the Smithsonian Institution of Washington in 

 accessible form, and accordingly they have been far too much ignored. 



* ' Scientific Writings of Joseph Henry,' vol. i, p. 201. Published hy the 

 Smithsonian Institution, "Washington, 1886. 



