678 TEXT-BOOK OF PHYSIOLOGY. 



2. As a Current Deflector. When it is desirable to deflect the current to 

 two pairs of electrodes differently situated, wires are carried from 

 binding posts 3 and 4 to one pair, and from 5 and 6 to the other pair. 

 The cross wires are then removed. According to the position of the 

 rocker the current will be deflected to one or the other. 

 The Indue torium. This is an apparatus designed for the purpose 

 of obtaining single or rapidly succeeding electric currents by induction. 

 Its construction is based on facts discovered by Faraday, some of which 

 are the following: 



If t\vo circuits, a primary and a secondary, are placed parallel to each 

 other, the former connected with a galvanic cell, the latter with a galvan- 

 ometer, it is found that, at the moment the primary circuit is made, and 

 at the moment it is broken, a current is induced in the secondary circuit, 

 as shown by a momentary deflection of the galvanometer needle. During 

 the continuous flow of the current through the primary circuit there is no 



FIG. 341. POHL'S COMMUTATOR. A. Arranged as a current reverser; B, as a cur- 

 rent deflector. 



evidence of a current in the secondary circuit. The induced current is 

 but of momentary duration. The current flowing through the primary 

 circuit is termed the inducing, the current flowing through the secondary 

 circuit the induced current. 



The induced current is opposite in direction to that of the inducing 

 current when the circuit is made or closed; it is in the same direction, 

 however, when the circuit is broken or opened. 



If the circuits are arranged in the form of coils, it is found that, other 

 things being equal, the strength of the induced currents w r ill be proportional 

 to the number of turns in the coils. 



If the coils are placed at varying distances from each other, the strength 

 of the induced current varies, increasing as the coils are approximated, 

 decreasing as they are separated. 



Approximation or separation of the coils while the current is flowing 

 through the primary circuit develops an induced current, which disappears, 



