PHYSIOLOGIC APPARATUS. 



679 



however, the moment the movement of the coil ceases. A sudden increase 

 or decrease in the strength of the inducing current also develops an induced 

 current. 



When the coils are approximated or the primary current increased in 

 strength, the induced current is opposite in direction to that of the inducing 

 current; with the reverse conditions, the induced current has the same 

 direction. 



The induced currents have been termed, in honor of their discoverer, 

 Faradic currents. 



The du Bois-Reymond inductorium, based on the foregoing facts, 

 consists essentially of two coils of insulated copper wire, termed primary 

 and secondary (Fig. 342). 



The primary 



coil, R', consists S 



of thick copper 

 wire wound 

 around a wooden 

 spool attached to 

 a vertical support. 

 The beginning of 

 this coil is at the 

 binding post S", 

 its termination 

 either at binding 

 post P" or S'". 

 In the course of 

 this primary wire 

 or circuit, there 

 are placed two 

 vertical bars of 

 soft iron, B', con- 

 nected at their 

 bases to form a 

 horseshoe magnet, 



around the ends of which the wire is coiled. The object of this device 

 will be explained later. 



Inside the primary coil there is placed a bundle of soft iron wires, 

 which, as soon as the circuit is made, become magnetized, with the effect 

 of increasing the action of the inducing current. 



The secondary coil, R", consists of a much greater number of turns 

 of a finer copper wire, the ratio being about 40 to i, also wound around a 

 spool, having a tunnel sufficiently large to enable it to slide over the pri- 

 mary. By these means the strength of the induced current is increased. 

 As a result of the construction of the inductorium, the low electro-motive 

 force of the cell is transformed into the high electro-motive force charac- 

 teristic of the induced current. As the number of turns of wire in the 

 secondary coil is to the number in the primary, so are the electro-motive 

 forces in the secondary coil to those in the primary coil. 



The secondary coil slides along a track, B, which permits it to be 



FIG. 342. INDUCTORIUM or DU BOIS-REYMOND. R', Pri- 

 mary, R", secondary spiral. B. Board on which R" 



moves, i. Scale. H . Wires from battery. P', P". 



Pillars. H. Neef's hammer. B'. Electro-magnet. S'. 

 Binding screw touching the steel spring (H). S" and 

 S'". Binding screws to which to attach wires where Neef's 

 hammer is not required. 



