4 6 



PHYSIOL OGICA L PHYSICS. 



[Chap. IV. 



basement line of the upper part ; bb is that of the 

 lower. Now when the primary circuit is closed, the 

 current from the battery should at once rise to its 

 maximum, which would be represented by the perpen- 

 dicular dotted line AB, but, owing to the extra current 



CLOSING 



OPENING 



--. 3' 



Fig. 25. Effects of the Extra Current on the Induction Currents* 



in the inverse direction, it attains its maximum com- 

 paratively slowly, as represented by the continuous 

 curved line 1. Simultaneously with the establish- 

 ment of the primary circuit is a secondary induced 

 current, represented by the curve 2, on the under side 

 of bb, because it is in the opposite direction to 1. 

 Again, on opening the primary circuit its current 

 is suddenly arrested, which is shown in the figure 

 by the perpendicular continuous line 3 3, unaffected 

 by any extra current because of the interruption 

 to the circuit. Corresponding to the opening is 

 an induced current in the secondary coil, which 

 suddenly attains its maximum, as represented by the 

 perpendicular 4 4, and then falls off more gradually, 

 as represented by the curved continuation of 4 4. 

 By this graphic method the difference between the 

 induced current of opening 2, and that of closing 4, 

 is plainly seen ; and this accounts for as great a 

 difference in the physiological effects of the two 

 induced currents, the effect of opening being always 



