the Magnetic Permeability of Nickel and Iron. 187 
In cases where a vacuum was employed the glass tube N 
could not be removed from the solenoid; hence the specimen 
was demagnetized by raising its temperature above the 
critical point, while compensation was made for the direct 
action of the solenoid when the metal was in the neutral state 
consequent on its high temperature. 
The intensity of magnetization I corresponding to a mag- 
netic force H being known, values of the susceptibility 
K (= a4 were calculated, and the permeability could then be 
deduced from the equation, 
w=4re+1. 
In fig. 4, each separate curve shows the relation between 
permeability and magnetic force for a particular temperature, 
Fig. 4, 
Permeability. 
10 20 30 40 ; 50 
Magnetic Force. 
and there is drawn one H curve for each temperature at which 
an experiment was made. In order to obtain from this series 
of curves the relation between permeability and temperature 
for any particular field, it is merely necessary to draw an 
