36 INDUCTION SHOCKS 
by the relative positions of the primary and secondary 
coils. M, the mutual induction between the primary 
and secondary coils, varies with changes in the position 
of the secondary relative to the primary, but is fixed for 
each position. It can therefore be determined once for 
each position of the secondary coil, and the values thus 
obtained used in all future calculations. 
Since mutual induction is the factor which varies 
with shifts in the position of the secondary coil relative 
to the primary, most of the calibrations hitherto pro- 
posed amount in effect to determinations of the relative 
mutual inductions for the various secondary positions. 
That the stimulating power should theoretically be pro- 
portional to the mutual induction so long as the other 
factors remain constant is obvious from inspection of the 
expression That the proportion really does exist 
j^i 
is proved by the experimental verification of the Fick, 
Kronecker, and Edelmann calibrations, as well as by the 
experiments carried out in the development of the pres- 
ent method.* 
L, the inductance of the secondary coil, is a function 
of the construction of the coil and is therefore constant 
for any given inductorium except as it is modified by 
extraneous influences. When the inductorium is used 
* Martin: Amer. Jour, of Physiol., 1908, xxii, p. 123. 
