Distribution of Energy by the Electric Current. 353 



transmitting electric energy would be limited only by the 



beat generated in it through electric resistance. 



In venturing to give expression to my thoughts upon this 

 subject , in my address to the Iron and Steel Institute in March 

 1877, I stated that a copper rod 3 inches in diameter would 

 be capable of transmitting energy to the extent of a thousand 

 horse-power an hour a distance of 30 miles, there to give 

 motion to electrodynamic engines, or to produce illumination 

 sufficient to light up a town with 250,000 candle-power. 



Although this statement was considered by many a bold 

 one at the time it was made, I now find that a conductor 

 such as I then described might be able to transmit three or 

 four times the amount of power then named, and that the 

 light producible per horse-power was also, according to our 

 present more advanced state of knowledge, very much under- 

 stated. 



No serious difficulty need be apprehended as to the pro- 

 duction of a current sufficient in amount to fill a conductor 

 of such large proportions as here indicated. Although it 

 would perhaps be impossible to construct a single dynamo- 

 electric machine of sufficient power for that purpose, any 

 number of smaller machines could be easily coupled up both 

 for intensity and quantity to produce the desired aggregate 

 amount. 



A difficulty would, however, arise at the other end, where 

 the electric energy was to be applied, and where it would 

 therefore be requisite to have an arrangement for its distri- 

 bution over a number of branch circuits, so that each might 

 receive such a proportion of the total current in the main 

 conductor as to produce the number of lights, or the amount 

 of power intended to be supplied. An accidental increase 

 of resistance in one or other of the branch circuits would 

 produce the double inconvenience of starving the circuits in 

 which such increased resistance had occurred and of supply- 

 ing an excess of current to the other circuits. 



In order to carry out such a system of supply, it would be 

 necessary to have the means of so regulating the current in 

 each branch circuit, that only a predetermined amount should 

 be allowed to flow through the same ; it would be desirable 

 also to furnish each circuit with the means of measuring and 

 recording the amount of electric current passed through the 

 same in any period of time. 



It is my special purpose to bring before you an instrument 

 by which these two purposes can be accomplished. The 

 current-regulator (as represented in Plate XII.) consists 

 principally of a strip of metal (of mild steel or fused iron by 



