DYNAMO-ELECTRIC MACHINES. 99 



whether the number of lamps in use be a part, or the whole to be 

 fed. To obviate this difficulty, it has been customary to supply 

 moderate sized machines to feed 3, 4, 5 or 6 lamps, and to put in 

 more than one machine where a greater number of lamps is required, 

 when a portion ot the whole is likely to be disused. 



In cases of dynamos for transmitting power, where the power 

 used varies, it is an obvious advantage if machines could be con- 

 structed to be self-regulating, and would simply absorb power from 

 the motor which would bear a constant ratio to the work done. 

 This would also apply to machines for electro-chemical purposes. In 

 an establishment containing a number of baths, for depositing one 

 metal, or for depositing several kinds, it would be a great advantage 

 if the machine was self-adjusting, so as to preserve the same electro- 

 motive force, no matter whether one or twenty baths were in use at 

 one time. 



It may be well to say a few words on the modifications 

 necessary in the construction of machines, to suit the varying con- 

 ditions under which they are to be applied. In their application to 

 electro-metallurgy, the resistance of the bath is so small, that 

 the question of the electro-motive force required is scarcely 

 necessary to be considered. It is different however with regard 

 to quantity. A machine might be capable of depositing the 

 same quantity of metal distributed amongst several baths, that it 

 could deposit in one only. But the same machine would not answer 

 for depositing a larger quantity amongst several baths, than the 

 amount it was designed to deposit, without the risk of being de- 

 stroyed. All machines however, are capable of varying the work to 

 be done, but only within the limits of the maximum amount for 

 which they were designed. If it was desired to deposit as much 

 metal in each of several baths as it was intended to be deposited in 

 one only by a machine, a larger one would be necessary. A large 

 machine will electro-plate a few articles as well as a great number, 

 but with nearly the same expenditure of power. The conditions 

 then of construction of dynamos for electro-chemical purposes, are 

 generally those of quantity only, and not of varying electro-motive 

 force and quantity of current together, as is necessary in those used 

 for most other purposes. 



In dynamos for the transmission of power, the circumstance of 



