Critical Points of Nickel and Iron. 395 



annealed iron wire 1 millim. in diameter. The wire was in the 

 first instance loaded with 12 kilos (the highest load employed 

 in the experiment), and was subjected to a magnetizing force 

 of 15*5 C.G.S. units which was alternately applied (always 

 in the same direction) and removed until the deflexions of the 

 ballistic galvanometer became constant. The load was then 

 entirely removed, and the same force was again applied and 

 removed as before. A load of 2 kilos was now put on the wire, 



Fi°r. 1. — Iron. 

 +io 



-20 



and the same operations were repeated witli tins and the sub- 

 sequent loads up to 12 kilos. Next the load was again entirely 

 removed, and a similar series of observations was made with a 

 magnetizing force of 10*5 C.G.S. units, and so on until the 

 force had diminished to 2*8. The entire set of experiments was 

 then repeated with ascending forces up to ] 5*5 ; this set did not 

 sensibly differ from the one taken with descending magnetizing 

 forces. As might be expected, each change of load produced 



* If P and P„ represent respectively the permeability with no load 

 and a load of n kilos, the percentage alteration of permeability is taken to 

 be 10 °(Po- r ^ or 10Q (Pn-P ) according- as the permeability is de- 



P o. * , 



creased or increased bv loading 



2 H 2 



