Prof. Thomson on the Electro-dynamic Qualities of Metals. 471 



galvanometer electrode had to be shifted over about 4^ inches on the 

 multiplying branch, towards the end of the testing conductor con- 

 nected with the nickel, that is to say, in such a direction as to indi- 

 cate a diminished resistance in the nickel. When the same opera- 

 tions were gone through with the nickel placed longitudinally be- 

 tween the poles of the electro-magnet, the zero-point on the multi- 

 plying branch was shifted about 6 inches in the direction which 

 indicated an increased resistance in the nickel. 



The piece of iron similarly tested, gave effects in the same direc- 

 tion in each case, and the results originally obtained for iron (§§ 146, 

 155, 161-177) were thus verified. 



No effect whatever could be discovered when the piece of brass 

 was similarly tried. It is much to be desired that experiments with 

 highly increased power, and with a better kind of galvanometer, 

 should be made, to discover whatever very small influence is really 

 produced by magnetic force on the comparatively non-magnetic 

 metals. 



The shifting of the neutral point on the multiplying branch, re- 

 quired to balance the effect produced by the longitudinal magnetiza- 

 tion m the iron, was only from 1^ to 2 inches. Three inches were 

 required to balance the opposite effect of the transverse magneti- 

 zation. 



Hence, with the same magnetic force, the effect of longitudinal 

 magnetization, in increasing the resistance, is from three to four times 

 as great in nickel as in iron ; but the contrary effect of transverse 

 magnetization is nearly the same in the two metals with the same 

 magnetic force. It may be remarked, in connexion with this com- 

 parison, that nickel was found by Faraday to lose its magnetic induc- 

 tive capacity much more rapidly with elevation of temperature, and 

 that it must consequently, as I have shown, experience a greater 

 cooling effect with demagnetization* than iron, at the temperature 

 of the metals in the experiment. It will be very important to test 

 the new property for each metal at those higher temperatures at 

 which it is very rapidly losing its magnetic property, and to test it 

 at atmospheric temperature for cobalt, which, as Faraday discovered, 

 actually gains magnetic inductive capacity as its temperature is 

 raised from ordinary atmospheric temperatures, and which, conse- 

 quently, must experience a heating effect with demagnetization, and 

 a cooling effect with magnetization. 



The actual amount of the effects of magnetization on conductivity, 

 demonstrated by the experiments which have been described, may 

 be estimated with some approach to accuracy from the preceding 

 data. Thus the value of an inch on the multiplying branch would 

 be the same as that of -J^ x ^, or J^^- of an inch on the portion of the 

 main testing conductor between its ends. The whole resistance of 

 this f of an inch of the main testing conductor, assisted by the 

 attached multii)lying branch of 36 inches, is of course less, in the 

 ratio of 48 to 49, than that of any simple f of an inch of the 

 testing conductor ; but in the actual circumstances there will be no 



* See Nichol's Cyclopasdia of Physical Science, article " Thenno-magiietism." 



