Mr. Henry Wilde on a 



On a Magnetometer for showing the Influence of 

 Temperature on the Magnetisation of Iron and 

 other Magnetic Substances. By Henry Wilde, 

 F.R.S. 



{Received October 2nd, 1894). 



It is not a little remarkable that, in this age of active 

 experimental research, there should be any doubt as to the 

 influence of temperature on the magnetic power of iron 

 and other magnetic substances ; yet, from the 17th century 

 to the present time, the most discordant opinions have 

 prevailed on this subject. Barlow, in the year 1822, found 

 that the magnetic power of bars of iron which he experi- 

 mented upon, as measured by the deflections of a compass 

 needle, increased with the temperature up to a dull red 

 heat, at which it was the strongest ; but, at a bright red 

 heat, all magnetic action of the iron suddenly disappeared.* 

 Scoresby, Christie, and others, have also noted a similar 

 increase in the magnetic power of iron with increase of 

 temperature, when measured by the same means. Faraday, 

 on the other hand, described experiments to show that the 

 magnetic power of iron diminished with, increase of tempera- 

 ture. He also found that iron at a bright red heat was not 

 entirely insensible to the action of large magnetising forces. 



More recently, Rowland^ and Hopkinson,]: by the 

 employment of electro-dynamic methods and the needle 

 indications of Barlow, have also found an increase in the 

 magnetic power of iron with increase of temperature. 



* Phil. Trans., 1822, p. 117. 



t Phil. Mag., 1874, Vol. LXVIIL, p. 321. 



% Phil. Trans., A, 1889, Vol. CLXXX., p. 443. 



