4 Mr. Henry Wilde on a 



comparatively low temperatures and with small magnetising 

 forces, yet, from the contradictory results which had been 

 obtained by other experimenters, directly opposite con- 

 clusions as to the magnetic intensities of the land and 

 ocean areas respectively might, with some show of reason, 

 be drawn from those which I had arrived at. The important 

 bearing which the influence of temperature has upon the 

 phenomena of terrestrial magnetism, induced me to under- 

 take an investigation into the causes of the conflicting 

 results hitherto obtained, with the hope, also, that I might 

 be able to extend still further our knowledge of magnetic 

 substances. 



The results of my experiments, which are embodied in 

 a paper read before the Royal Society,* confirm the 

 general law of the diminution of the magnetisation of 

 magnetic substances with increase of temperature for small 

 as well as for large magnetising forces. I have also 

 demonstrated in this paper that the apparent increase of 

 the magnetic power of heated iron, magnetite, and nickel is 

 so small as to be a negligible quantity in general magnetic 

 phenomena and terrestrial magnetism, and is due to a 

 surface resistance of these substances which disappears — 

 (i) on the application of heat ; (2) by the action of strong 

 magnetising forces ; (3) by diminishing the mass of the 

 magnetic substance acted upon by the magnetising force. 



I have further shown that the surface resistance of 

 cobalt at normal temperatures is so great, as to require a 

 tractive force equal to 373 lbs. per square inch, acting on a 

 minute quantity of the metal, to overcome it. 



The general results of my experiments have been con- 

 firmed by M. P. Curie, in two able papers in the Comptes 

 Rendus of the French Academy for April and May of 

 the present year. M. Curie also agrees with my conclusion 



* Proc. Roy. Soc, June 11, 1891. 



