.S7A' WILLIAM .S//..J//..V.V, FJUi. 



2 19 



engine is 2'G horse-power, so that but a small margin of JM aver IK 

 needed to suffice for the greatest possible requirement. 



.">. That the maximum energy which can be injuriously trans- 

 ferred into heat in the machine itself is 1/8 horse-power, so that 

 there is no fear here of destroying the insulation of the helix by 

 <sive heating. 



('.. That the maximum current is approximately that which 

 would be habitually used, and which the commutator and collecting 

 I irushcs are quite capable of transmitting. 



Hence I conclude that the new machine will give a steadier 

 light than the old one, with greater average economy of power, 

 that it will be less liable to derangement, and may lie driven 

 without variation of speed by a smaller engine ; also that the new 

 machine is free from the objection of having its currents reversed 

 when used for the purpose of electro deposition. 



The same peculiarity also enables me to effect an important 

 simplification of the regulator to work electric lamps, to dispense 

 with all wheel and clock-work in the arrangement, as shown in 

 Plate 21. The two carbons, being pushed onward by gravity 

 or spring power, are checked laterally by a pointed metallic 

 abutment, situated at such a distance from the arc itself that the 

 heat is only just sufficient to cause the gradual wasting away of 

 the carbon in contact with atmospheric air. The carbon holders 

 arc connected with the iron core of a solenoid coil, of a resistance 

 equal to about fifty times that of the arc, the ends of which coiF 

 are connected with the two electrodes respectively. The weight 

 of the core, which has to be maintained in suspension by the 

 attractive force produced by the current, determines the distance 

 Between the electrodes, and hence the electric resistance of the arc. 

 The result is that the length of the arc is regulated automatically 

 so as to maintain a uniform resistance, signifying a uniform 

 development of light. 



