COMPARISON OF ONE COIL WITH ANOTHER 51 
inductance of the coil, A its mean cross section, W the 
number of turns of wire composing it, and / its 
length. 
When, in the course of developing this method of 
measuring stimuli, the attempt was made to apply the 
above expression for L in the formula - > the curious ob- 
it 
servation resulted that it applied perfectly with some 
inductoria and not with others. That is to say, when 
equal stimuli were generated by means of different in- 
ductoria, equal values of were given by some, but 
LJ 
not by all, of the instruments compared. Upon analyz- 
ing the reason for the difference the following fact came 
out clearly; equal values of were given by those in- 
j_j 
ductoria whose secondary coils had the same number of 
turns of wire per centimeter of length, regardless of the total 
number of turns of wire; unequal values were given by 
those inductoria whose secondaries had different numbers 
of turns per centimeter of length. If we look now at the 
AW 2 
expression for L given above, i.e., L = > and sepa- 
rate within it the factor of turns per unit of length, the 
W 
expression reads L = AW X The experimental re- 
sults showed as stated above that in all the inductoria 
