549 



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 -r x f , or -^ of an inch on the portion of the 

 main testing conductor between its ends. The whole resistance of 

 this -^ of an inch of the main testing conductor, assisted by the 

 attached multiplying 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 

 loss of accuracy in neglecting so small a difference. Hence the 

 effect of the transverse magnetization of the^nickel was to diminish 

 its resistance in the ratio of half the length of the testing conductor 

 diminished by -il of an inch, to that of the same increased by the 

 same, that is to say, in the ratio of llfi to 12-^L, or of 383 to 385. 

 Hence it appears that the resistance of the nickel, when under the 

 transverse magnetizing force, was less by T L, and similarly, that 

 the resistance, when under the longitudinal magnetizing force, was 

 greater by y^j, than when freed from magnetic influence ; and 

 that the effects of the transverse and of the longitudinal magneti- 

 zing forces on the iron were to diminish its resistance and to in- 

 crease its resistance by -^ and -^ respectively. The first effect 

 which I succeeded in estimating ( loo) amounted to only ^g , 

 being the increase of resistance in an iron wire when longitudinally 

 * See Nichol's Cyclopaedia of Physical Science, article ' Thermo-magnetism.' 



