210 THE SCIEN7^IFIC PAPERS OF 



occurred to me that large amounts of energy, produced by means 

 of the dynamo-electric current-generator, might be conveyed 

 through a metallic conductor, such as a rod of copper fixed upon 

 insulating supports. Such a conductor would no doubt be expen- 

 sive ; but, if once established, the cost of maintenance would be 

 very small, and its power of transmitting electric energy would be 

 limited only by the heat 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 a distance of 30 miles, there to give motion to electro- 

 dynamic 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 know- 

 ledge, very much understated. 



No serious difficulty need be apprehended as to the production 

 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 suffi- 

 cient 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 distribution 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 

 supplying an excess of current to the other circuits. 



* Published in Vol. III. of the Scientific Papeis of Sir William Siemens, F.E.8. 



