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cuits be placed parallel to each other, as in the case of the 

 planes of two spirals or coils of the inductoriutn, the one wire 

 primary (P), being connected with a source of electricity 

 (battery), the other, the secondary (S), being- simply a closed 

 circuit ; whenever the P circuit is closed (made), or is opened 

 (broken), currents will at those moments be induced in the S 

 circuit. 



The make induction current flows in the S circuit in a direc- 

 tion opposite to that of the P circuit : whilst the break induction 

 current flows in the same direction as the original battery 

 current. 



These induction currents are of very short duration. 



Fig. 12 



Fig. 12, showing the direction of the make and break currents. In the sec- 

 ondary circuit the direction of the break current is shown by the dotted line and 

 arrow, and the make by the continuous line. 



Place the induction machine lengthwise in front of you 

 on the table with the interrupter turned to the right. In the 

 DuBois Reymoad type the wires are wound into two separ- 

 ate coils ; the P coil which is supported by a wooden upright 

 attached to the base of the instrument is composed of relatively 

 thick wire, while the S coil mounted upon a sliding foot is 

 composed of very thin wire, in this case invisible, as it has a 

 protective covering of vulcanite. 



The parallelism of the wire in the two coils is maintained 

 so long as the axes of the coils coincide. The successive turns 

 of the wire in each coil are also practically parallel to each 

 other. The P coil is provided with a core of soft iron wire 

 which magnetizes when a current passes in the surrounding 

 wire, an electro-magnet being thus produced. 



The electrical field produced by the coil is greatly intensi- 

 fied by this core, and the effect on the S coil is correspondingly 

 increased. The nearer the S coil is to the P coil, the more 

 powerful will be the induction currents. 



