METHODS OF ELECTRICAL STIMULATION 63 



Draw a diagram of the primary circuit, indi- 

 cating the connections of the inductorium. 



Empirical Graduation of Inductorium. Con- 

 nect the secondary coil with the galvanometer. 

 Join the primary coil to a dry cell, interposing a 

 simple key. Turn the secondary coil on its pivot 

 until it is at right angles with the primary coil. 

 Close the circuit. 



The galvanometer needle will not swing. 

 There is no induced current. 1 



Turn the secondary coil on its pivot, closing 

 the key from time to time to test the induction. 



The strength of the induction increases ap- 

 proximately as the cosine of the angle between 

 the coils increases. An empirical graduation is 

 sometimes placed on a circular scale beneath the 

 coil. 



When the axes of the two coils lie in the same 

 plane, slide the secondary towards the primary, 

 making and breaking the primary current from 

 time to time. 



The potential of the primary upon the second- 

 ary coil, i. e. the sum of the inductions of each 

 element of the primary upon all the elements of 

 the secondary coil, increases as the secondary is 

 brought nearer the primary coil. The increase is 

 not linear. As the distance between the coils 



i It is difficult to place the coil precisely at an angle of 90. 



