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



Table II. 



The principal feature of interest in the table is the same inversion 

 of the magnetic power of the heated cube of cobalt, in relation to 

 iron and nickel, as was obtained by the minute force of the magneto- 

 meter needle acting upon the small prism of the same metal. The 

 increase of the magnetic power of the heated cube was, however, 

 much greater relatively with smaller magnetising forces ; for, while 

 the ratio of increase with .20 amperes of current was as 1 : 1'15 

 between 13 C. and 442 C., the ratio with 3 amperes was as 1 : 1*6 

 between the same temperatures. 



The abruptness of the change in the magnetic condition of iron, 

 nickel, and cobalt, observed by Faraday,* at what is now aptly 

 termed the critical temperature, is also well seen in the table. 



Following up the results of the experiments which showed that 

 the apparent increase in the magnetic power of heated iron was 

 dependent upon the mass in relation to the magnetising force, it 

 appeared to me that heated cobalt might show a diminution of mag- 

 netic power, as in the case of iron and nickel, if a sufficiently large 

 magnetising force were brought to bear upon a minute quantity of 

 the metal, notwithstanding that it had so far shown an increase of 

 power for large, as well as for small, magnetising forces. 



A minute cylinder of cobalt, 0'06 inch long, O'Oo inch in diameter, 

 and grain in weight, was formed from a piece of the same cube of 

 the metal nsed in the previous experiments. A small hole was 

 drilled up the end of a thick piece of copper wire in the direction of 

 its axis, into which the cylinder of cobalt was driven tightly for 

 nearly the whole of its length. An eye was formed at the other end 

 of the copper wire for suspending the cobalt over the electro- 

 magnet. 



Similar cylinders of iron and nickel were formed from the cubes 



* 'Phil. Mag.,' 1836, vol. 8, p. 177; ibid., 1845, vol. 27, p. 1. 



