222 C. A. Perkins — Magnetic Permeability of Nickel. 



may have been due to a departure from the above law which 

 takes place on approaching the limit. 



The same thing has since been observed by Fromme, who 

 made use of the same method and ascribed the result to the 

 latter cause. 



In these experiments Eowland also investigated the magnet- 

 ism of nickel and a law for the variation of ji was discovered 

 similar to that holding in the case of iron. More recently* 

 he has made further experiments on nickel and ha^s added 

 cobalt to the list of substances following the same general law. 

 On account of the difficulty of procuring these metals in a pure 

 condition, fewer experiments have been made with them than 

 with iron, but the results, as far as found, agreed with those 

 for iron. 



In 1853 Pliickerf experimented on a large number of bodies, 

 and although the experiments were complicated by using an 

 electro-magnet as the magnetizing force, he attempted, as far as- 

 possible, to eliminate this effect by using the law of increase in 

 the case of iron. Only a few points were determined to fix the 

 curve of magnetization, but the results found showed that all 

 the substances experimented on approached a definite maxi- 

 mum which for iron, nickel and cobalt was relatively : Fe 1000, 

 Co 918, Ni 322, values which are in very good agreement with 

 those since found. 



Arndtsen^: also, using Weber's diamagnetometer, found that 

 nickel soon approached a maximum magnetization and reduc- 

 ing the values to absolute measure stated that for very weak 

 magnetizing forces the magnetism of nickel was five times that 

 given by Weber's formula for iron. 



All the experiments above mentioned were made at ordinary 

 temperatures, but Faraday§ found that by heating in olive oil, 

 the electro-magnetic properties of iron were hardly changed. 

 Nickel suffered a considerable decrease, while cobalt increased 

 in heating. 



The later experiments by Rowland, referred to above, were 

 made especially with reference to this point and show a very 

 interesting property of nickel, viz : that for weak magnetiz- 

 ing forces its permeability is much increased by heating from 

 15° to 220° Centigrade, while for stronger forces it is decreased. 

 The effect on iron is slight and cobalt has its permeability in- 

 creased for all magnetizing forces used, showing the accuracy 

 of Faraday's conclusions. 



More recent experiments by Fromme, Riecke, Bttinghausen 

 and others have confirmed the accuracy of these conclusions 

 and at the same time have developed new facts in relation to 

 the subject. 



*Phil. Mag.. November, 1874. fPogg. Ann., rol. xci. 



\ Pogg. Ann., vol. civ. § Exp. Res., xxx, 3424, 1855. 



