178 Lord Armstrong. On a Multiple Induction 



iehed increment of output. In fact, -when all the six were in action, 

 I only got about three times the output I obtained from one. 

 some time before I discovered the cause of this apparent anomaly ; 

 but at last I traced it to the recoil currents from the condensers, 

 which at each interruption of the primary current had to pass through 

 the battery in the reverse direction of the battery current. Thus a 

 conflict of currents was produced in the primary circuit, which 

 checked the acquisition of magnetism by the coils. I saw no remedy 

 for this interference, except the application of a separate battery to 

 each coil, and I accordingly exchanged my single battery of seven 

 large cells for six independent batteries composed of the same number 

 of cella proportionately reduced in size, and when this was done I 

 obtained the full measure of effect. 



Side by side with the multiple contact breaker I have a mechanical 

 contact breaker, in which the interruptions are effected by insulated 

 cam wheels fixed on a revolving shaft, which is fitted with spur gear 

 for high velocities. This mode of breaking contact has the advantage 

 of causing the sparks to be delivered in regular sequence, with equal 

 intervals between them. It also enables the exact number of dis- 

 charges per second to be ascertained ; but the automatic interrupter 

 gives a larger output, owing, I suppose, to the fact that each break 

 of contact takes place exactly at the moment when the magnetisation 

 of the coil is matured, whereas with the mechanical break the same 

 degree of coincidence cannot be attained. The six coils are placed 

 vertically beneath an ebonite table, through which the connecting 

 wires are conveyed in strong glass tubes, which also serve as pillars 

 for supporting the sparking points. These points are adjustable for 

 any required length of spark, and they operate in a radial direction 

 against a metallic conductor surrounding an ebonite disc, which, by 

 means of an india-rubber band and multiplying gear, can be very 

 rapidly rotated; and, whether it be at rest or in motion, it serves as 

 a collector, from which the united output of the coils can be drawn 

 off. By rotating the wheel and conveying the current through a 

 series of Greissler tubes fixed upon it in various positions, extremely 

 brilliant symmetrical figures can be produced, but for all other 

 purposes rotation is dispensed with, except to the extent of slight 

 movements to regulate the length of spark without altering the 

 adjustment of the points. A switch-board is provided for the purpose 

 of regulating the number of coils to be thrown into action, so that 

 they can be used singly or in any required number. 



The power of this apparatus as indicated by the voltameter is much 

 greater than that of the large hydro-electric machine made for the 

 Polytechnic Institution, but it is very inferior to it in regard to length 

 of spark, to which, however, I attach but little importance. I find it 

 well adapted for experimental investigation, and I have obtained with 



