Royal Society. 469 



a G-inch spark was obtained, but at the same time strong dis- 

 charges took place from the inner portion of the coil to the 

 glass cover; and there is little doubt that, had the experiment 

 been continued, the glass would have been perforated. With 

 three coils I have as yet ouly obtained a spark of 12^ inches in 

 length ; but, for the reasons already named, I shall probably 

 not venture to excite the coil to its greatest intensity. 

 I am. Gentlemen, 



Your obedient Servant, 



John P. Gassiot. 



LX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 400.] 



June 18, 1857. — The Lord Wrottesley, President, in the Chair. 



T^HE following communications were read : — 



*- " On the Development of CamwMS M««as." By Spence Bate, 



Esq., F.L.S. 



" On flie Electro-dynamic Qualities of Metals : — Effects of Mag- 

 netization on the Electric Conductivity of Nickel and of Iron." By 

 Professor W. Thomson, F.R.S. 



I have already communicated to the Royal Society a description 

 of experiments by which I found that iron, when subjected to mag- 

 netic force, acquires an increase of resistance to the conduction of 

 electricity along, and a diminution of resistance to the conduction of 

 electricity across, the lines of magnetization*. By experiments more 

 recently made, I have ascertained that the electric conductivity of 

 nickel is similarly influenced by magnetism, but to a greater degree, 

 and with a curious difference from iron in the relative magnitudes of 

 the transverse and longitudinal effects. 



In these experiments the effect of transverse magnetization was 

 first tested on a little rectangular piece of nickel \-2 inch long, •.')2 

 of an inch broad, and -12 thick, being the "keeper" of the nickel 

 horse-shoe (§ 143) belonging to the Industrial Museum of Edin- 

 burgh, and put at my disposal for experimental purposes through 

 the kindness of Dr. George Wilson. Exactly the method described 

 in § 175 of my previous communication referred to above, was fol- 

 lowed ; and the result, readily found on the first trial, was as stated. 



The effect of longitudinal magnetization on nickel was first found 

 with some difficulty, by an arrangement with the horse-shoe itself, 

 and magnetizing hehx (§ 143), the former furnished with suitable 

 electrodes for a powerful current through itself, and the system 

 treated in all respects (including cooling by streams of cold water) 

 as described in § 156, for a corresponding experiment on iron. The 



* See PhiL Trans. Bakerian Lecture, " On the Electro-dynamic Qualities of 

 Metals," Feb. 27, 1H56, § 140 of Part 4 and Part 5. In the present conununica- 

 tion that paper will be referred to simply by the sectional (§) numbers. 



