THE CHARACTERISTICS OF INDUCED CURRENTS 9 
tance within the primary coil. This phenomenon may be 
explained as follows : When the current sweeps through 
any turn of wire of the primary coil it tends to establish 
a field of force about that turn; but as the lines of force 
composing this field cut through adjacent turns of wire 
of the primary they induce currents therein. Since en- 
ergy is expended in this inductance the currents thus 
induced cannot be in the same direction as the inducing 
current; inasmuch as if they were, there would be a 
A B 
FIG. 3. Curve illustrating the growth and decline of a make 
induced current. AB represents the time required for the primary 
current to become fully established. 
gain of energy a thing impossible ; they oppose the in- 
ducing current and allow it to reach its full value only 
after it has yielded the energy necessary for the induc- 
tance. In Fig. 3 the line AB represents the time occu- 
pied by the primary current in establishing itself against 
the inductance, and therefore the time during which the 
induced current increases. 
Any condition which diminishes the inductance within 
the primary coil, thereby allowing the primary current 
to establish itself more quickly, will not only make the 
