46 INDUCTION SHOCKS 
y 
To derive the equation for obtaining / computed when 
I observed is known we determine in a series of experi- 
ments the ratios of / computed to 7 observed (see column 
4 of the table). If now the decimal part of each ratio is 
divided by its corresponding value of 7 observed, a con- 
stant is obtained which represents the number by which 
7 observed must be multiplied to obtain this decimal part 
of the ratio. This constant is shown in column 5. 
After the constant is found it is used for computing 7 
according to the formula T r = 7o X (i + KI ). In this 
formula 7 C is the computed value of 7, 7o is its observed 
value, and K is the constant, in the case cited in the 
table equaling .22. 
The method of correcting for the magnetization of 
the iron core is given in detail since, in spite of the abun- 
dant theoretical justification for the omission of the 
iron core, especially where quantitative estimations are 
sought, for the practical purposes of the physiologist 
the inductorium as commonly used, with the iron core 
present, is usually to be preferred. The intensity of 
stimulus, other factors being equal, is at least five times 
greater with the iron core than without it in inductoria 
of the usual type. This increased efficiency makes it 
possible to obtain with primary currents of moderate 
intensity as strong stimuli as the physiologist ordinarily 
requires. The use of moderate primary currents is of 
great importance in quantitative estimations of indue- 
