110 Mr. H. Wilde. On the Influence of Temperature [June 11, 



the magnetic power of iron with increase of temperature. 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, that the power 

 diminished for large magnetising forces with ascending tempera- 

 tures. 



Rowland extended his observations to the magnetisation of nickel 

 and cobalt, and found that the magnetic behaviour of these metals 

 with increase of temperature was the same as that observed in 

 iron. 



Experiments have also recently been made by Professor Riicker* 

 on the effects of temperature on the natural magnet (magnetite), and 

 he has found, by means of an extremely sensitive instrument, that 

 the magnetic power of this mineral increases as the temperature 

 rises, as in the case of iron. 



The important bearing which the influence of temperature has upon 

 the phenomena of terrestrial magnetism induced me to undertake 

 an investigation into the causes of the conflicting results obtained by 

 those physicists who have preceded me in this research, with the hope 

 also that I might be able to extend still further our knowledge of 

 magnetic substances, especially in their relation to terrestrial 

 physics. 



The apparatus used in the investigation consisted of a bar electro- 

 magnet, formed of a cylinder of iron 24 inches in length and 3 '5 

 inches in diameter. The electro-magnet was placed in a vertical 

 position, with its lower end screwed firmly into a massive base of 

 cast iron. The upper end of the core was furnished with a short 

 cylinder of iron, of the same diameter as the core, and -having a 

 conoidal termination, which constituted the pole of the magnet. 



The magnetometer was a plain cylindrical needle, 4 inches long 

 and O13 inch in diameter, suspended from a single fibre of un- 

 twisted silk. The needle received a charge of magnetism sufficient 

 to support fourteen times its own weight from either pole, and was 

 thickly covered with spun silk to prevent the weakening of its magr 

 netism by close proximity to the heated substances under examina- 

 tion. 



The iron experimented upon was a cylindrical bar of good mal- 

 leable iron, 6 inches long and 0*7 inch in diameter. One end of 

 the iron bar was drilled through its diameter to receive a strong iron 

 pin, which projected crosswise on each side of the bar for the purpose 

 of dropping it readily, when heated, into a stirrup placed over the 

 electro-magnet. Several of these bars were prepared from the same 

 rod of iron, to replace those which were reduced in thickness by 

 fusion and oxidation, as well as for other experiments. 

 * ' Eoy. Soc. Proc.,' 1890, vol. 48, p. 522. 



