8 INDUCTION SHOCKS 
angles to the primary no lines of force pass lengthwise 
through it. For quantitative purposes, however, it is 
better to have a rather long slide and to keep the sec- 
ondary coil always with its axis coincident with that of 
the primary. 
The Form of Make and Break Induced Currents. 
When a circuit is closed through the primary coil of an 
inductorium there is a growth of the current within this 
coil from zero to its full value. Coincidently with this 
growth of current there is being established a field of 
force about the coil, and if there is a secondary coil 
within this field a current is being induced therein. 
This induced current also begins at zero and increases 
in intensity during the establishment of the field of 
force about the primary. As soon as the field is fully 
established, so that movement of the lines of force 
ceases, there is no further induction and the current 
within the secondary dies away. We may represent the 
successive changes in intensity of the induced current 
by a curve such as that shown in Fig. 3 in which the 
height of the curve at any point represents the intensity 
of the induced current at that instant. 
The rise of the make induced current from zero to the 
maximum, although rapid, is by no means instantaneous, 
there being a well marked delay in the establishment of 
the -current through the primary coil after the circuit is 
closed. This delay is due to the phenomenon of indue- 
