ELECTRICAL CONSIDERATIONS. 



Induction machine. Du Bois Raymond's Inductorium. 



Principle of action : If portions of the wires forming two separate 

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

 of the two spirals or coils of the Inductorium (Fig. 25), the one wire, 



FIG. 25. Induced currents are only shown in S. The solid arrows indicate 

 the direction of the currents at closure of key K. Dotted arrows at break. 

 Similar currents occur in P and at the same time. 



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 direction 

 opposite to that in 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. 



Place the induction machine lengthways in front of you on the 

 table with the interrupter turned to the right. 



In the Du Bois Reymond type the wires are wound into two 

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

 attached to the base of the instrument is composed of relatively thick 

 wire, whilst 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 wire in each coil are also practically 

 parallel to each other. 



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

 magnetises when a current passes in the surrounding wire an electro- 

 magnet being thus formed. 



The electrical field produced by the coil is greatly intensified 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. 



