1.891.] upon the Magnetisation of Iron and other Substances. 117 



experimented with, and mounted for suspension over the electro- 

 magnet in the same manner as the cylinder of cobalt. 



The flat end of the electro-magnet was surmounted by a cone of 

 iron 4 inches high and 3 inches in diameter at the base, with the apex 

 rounded to form a pole 0*1 inch in diameter. 



As a test of the magnetic intensity at the pole of the electro- 

 magnet, the little cylinder of iron was suspended from the balance, 

 when the tractive force was 0-601 Ib. with 20 amperes of current, 

 which is equal to 305 Ibs. per square inch of section, or more than 

 17,000 times the weight of the iron. 



When the cobalt was submitted to the same magnetising force as 

 the iron, the tractive force at 13 C. was 0'304 Ib., which is equal to 

 154 Ibs. per square inch of section, or 8000 times the weight of the 

 cylinder of cobalt. 



On heating the cobalt, whilst suspended over the electro-magnet, a 

 constant diminution of the magnetic power of the matal was now 

 observed from 13 C., as in the case of iron and nickel, the tractive 

 force diminishing from 0'304 Ib. at 13 C. to 0-296 Ib. at 442 C. 



The results of the experiments with the minute cylinders of the 

 magnetic metals are given below : 



% 



Table III. 



That the property of the anomalous increase of the magnetic power 

 of the heated cobalt was broken down by the intensity of the mag- 

 netic force and the diminution of the mass conjointly, as in the case 

 of the small and large bars of iron, was further shown by submitting 

 the little cylinder of cobalt to the action of the electro- magnet excited 

 by 5 amperes of current, when the tractive force of the heated cobalt 

 was increased from 0'140 Ib. at 13 C. to 0'156 Ib. at 442 C. 



