Magnetometer for showing the Influence of Temperature. 3 



These experimenters were, however, the first to recognise 

 that the apparent increase of the magnetic power of iron, 

 up to the dull red heat, only held good for small magnetising 

 forces, and, further, they found with Faraday, that the 

 power diminished for large magnetising forces with 

 ascending temperatures. Rowland extended his observa- 

 tions to the magnetisation of nickel and cobalt, and found 

 that the magnetic behaviour of these metals with increase of 

 temperature was the same as he had observed in iron. 



Experiments have also recently been made by Rlicker 

 on the effects of temperature on the natural magnet 

 {magnetite), and he has found that the magnetic power of 

 this mineral apparently increases with ascending tempera- 

 ture. A later pronouncement on this subject was made by 

 the President of the Royal Society (Sir G. G. Stokes) in 

 the year 1890, in the course of his anniversary address, in 

 which he stated that, it was generally believed that the 

 susceptibility or magnetisation of iron decreased with the 

 temperature, but, on the contrary, it had been recently 

 found that the susceptibility was enormously increased with 

 ascending temperatures.* This generalisation was after- 

 wards limited, through my representations, to the action of 

 small magnetising forces.f 



In my paper on " The Unsymmetrical Distribution of 

 Terrestrial Magnetism,";}; it was shown that by heating 

 small surfaces of the thin sheet iron covering the ocean 

 areas of the mapped globe, strong polarity was induced at 

 the junction of the heated parts, just as when the magnetic 

 continuity of the iron was interrupted by cutting through 

 the same parts of the iron in an equatorial direction. 

 Although this experiment appeared to me to demonstrate, 

 conclusively, that the magnetic power of iron was reduced at 



* Nature, Dec. nth, 1890. 



t Proc. Roy. Soc, Dec. 1st, 1890. 



% Proc. Roy. Soc, Jany. 22nd, 1891. 



