396 MEMORIAL OF JOSEPH HENRY. 



" 13. Little or no increase in the effect is produced by inserting a 

 piece of soft iron into the center of a flat spiral. 



"14. The effect produced by an electro-magnet, in giving the 

 shock, is due principally to the coiling of the long wire which sur- 

 rounds the soft iron." * 



Note F. (From p. 255.) 



OSCILLATION OF ELECTRICAL DISCHARGE. 



Sir William Thomson, in 1853, indicated the probability of an 

 oscillatory character in the electrical discharge; remarking: "It 

 appears to me not improbable that double, triple, and quadruple 

 flashes of lightning which I have frequently seen on the continent 

 of Europe, and sometimes though not so frequently in this country, 

 (lasting generally long enough to allow an observer after his atten- 

 tion is drawn by the first light of the flash, to turn his head around 

 and see distinctly the course of the lightning in the sky,) result from 

 the discharge possessing this oscillatory character. - - - The 

 decomposition of water by electricity from an ordinary electrical 

 machine, in which, as has been shown by Faraday, more than the 

 electro-chemical equivalent of the whole electricity that passes, 

 appears in oxygen and hydrogen rising mixed from each pole, is 

 probably due to electrical oscillations in the discharges consequent 

 on the successive sparks." f 



In a foot-note at this point of the paper, the eminent physicist 

 adds: "This explanation occurred to me about a year and a half 

 ago, in consequence of the conclusions regarding the oscillatory 

 nature of the discharge in certain circumstances, drawn from mathe- 

 matical investigation. I afterward found that it had been sug- 

 gested as a conjecture by Helmholtz in his Erhaltung der Kraft, 

 (Berlin, 1847,) in the following terms: 'It is easy to explain this 

 law, if we assume that the discharge of a battery is not a simple 

 motion of the electricity in one direction, but a backward and for- 

 ward motion between the coatings, in oscillations which become 

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

 of the resistances. The notion that the current of discharge con- 

 sists of alternately opposed currents is favored by the alternately 

 opposed magnetic actions of the same; and secondly by the phe- 

 nomena observed by Wollaston while attempting to decompose 



* Journal of the Franklin Institute, March, 1835, vol. xv. pp. 169, 170. 

 t L. E. D. Phil. Mag. June, 1853, vol. v. pp. 400, 401. 



