Mr. R. H. M. Bosanquet on Practical Electricity. 251 



The simplest mode of effecting the charge is to charge in 

 one series, starting by means of a resistance-wire in parallel 

 circuit, thus : — A wire of 5 or 6 ohms resistance, arranged so 

 that it can become red-hot without injury, is introduced be- 

 tween the terminals, and the machine driven at full speed. 

 A difference of tension is thus produced between the ends of 

 the wire, which must be greater than that of the accumulators 

 to be charged. This difference amounts with my machine to 

 70 or 80 volts, or even more. Then, if we have 80 volts and 

 6 ohms of wire, we get a current of a little over 13 amperes, 

 which is enough to excite the machine well. 



The terminals of the battery are now joined up to the 

 terminals between which the difference of tension is estab- 

 lished, + to + if the machine is straight, + to — if reversed. 

 The existing difference of tension drives back the battery- 

 current, and a charging-current is set up. With the 30 cells 

 in series I find that the current traversing the accumulators 

 is* about 10 amperes under these circumstances. 



I Accumulators 1 



I 



Wi 



_ | 

 Magnets — Armature — Magnets 



The machine is then traversed by the double current of 

 more than 20 amperes from both battery and resistance- 

 wire. Great statical resistance to the engine is consequently 

 developed, and the magnets are well excited ; but the current 

 through the 6-ohms wire goes to waste, and in fact the wire 

 is kept nearly red-hot. A large power is required to maintain 

 this state of things. The last step is to remove the wire, 

 leaving the battery with the current of about 10 amperes 

 passing through it. The resistance at the machine is reduced 

 to about one fourth by the halving of the current, and the 

 engine quickens its speed ; but, on the other hand, in order 

 to maintain the difference of over 70 volts when excited only 

 by 10 amperes, the machine requires a high speed. 



Consequently there is a period of instability at the moment 

 of removing the resistance, and the machine is often reversed 

 before the high speed is established. The only means of 

 obviating this are (1) to cram on every available pound of 

 steam at the moment, (2) to execute the two operations of 

 joining up the battery and removing the resistance in such 

 quick succession that the speed has not time to fall. By the 

 use of both these precautions I have generally succeeded in 



