THE INDUCTION COIL 



9 



connect the pillar d (fig. 6) with the binding screw / by a stout wire 

 and screw up the screws Sj and s 2 (fig. 10) until S] is removed from 

 contact with the spring v, ands 2 lies just below it, but not touching it. 

 Fig. 10 illustrates the action of the hammer with this arrangement. 

 The connections to the battery remain the same. On closing the key 

 k the path of the current is now from the battery to the pillar A, and 

 from this by the stout wire to the screw s,, and thence to the primary 

 coil p c. From the primary coil it passes to the electromagnet e, thence 

 to the pillar B, and so through 

 the key k back to the battery. 

 Immediately the current is 

 closed the electromagnet at- 

 tracts the armature of the 

 spring v, and as it pulls it down 

 brings the platinum plate on its 

 lower surface into contact with 

 the platinum point of the screw 

 s 2 , the result of which is that 

 the derived circuit from the 

 pillar a through the spring v to 

 the pillar b is closed. The 

 current is now divided, and in- 

 stead of all passing through the 

 primary coil and electromagnet 

 most travels through the derived 



circuit, because the resistance of this is much less than that of the coil 

 and electromagnet. The current of the electromagnet becoming so 

 much weaker is now unable to resist the upward pull of the spring v, 

 which therefore recoils, and thus breaks its contact with the screw S 2 . 

 The derived circuit is broken and the whole current again sent through 

 the coil, the cycle is repeated, and so on continuously. 



Just as in the previously described case where a simple derived 

 circuit was used to equalise the make and break shocks this arrange- 

 ment attains the same end, and is to be used when it is necessary 

 that the two shocks should be nearly equal. 



One of the great conveniences of the sledge inductorium is the 

 ready manner in which the strength of the induced shock can be 

 varied by simply altering the distance of the secondary coil from the 

 primary. It must, however, be remembered that the strength of the 

 induced current is by no means inversely proportional to the distance 

 of the secondary coil from the primary, but that the strength of the 

 induced current increases at a far greater rate than the diminution of 



Fig. 10. — To Illustrate the Action of 

 Neef's Hammer with the Helmholtz 

 Modification. 



