THE CONQUEST OF NATURE 



wasted power of Niagara, that a thousand horse- 

 power might be transmitted a distance of, say, thirty 

 miles over a copper rod three inches in diameter. But 

 a copper rod three inches in diameter is enormously 

 expensive, and when Siemens further stated that sixty 

 per cent of the power involved would be lost in trans- 

 mission, it was obvious that the method was far too 

 wasteful to be commercially practicable. 



For a time the experimenters with the transmission of 

 electricity along a wire were on the wrong track. They 

 were experimenting with a continuous current which, 

 as we have seen, is produced from an ordinary dynamo 

 with the aid of a commutator. But hosts of experiments 

 finally made it clear that this form of current, no matter 

 how powerful it might be, is unable to traverse consider- 

 able distance without great loss, being frittered away in 

 the form of heat. 



But the very term "continuous current" implies the 

 existence of a current that is not continuous. In point 

 of fact, we have already seen that a dynamo, if not sup- 

 plied with a commutator, will produce what is called an 

 alternating current, and such a current has long been 

 known to possess properties peculiar to itself. It is, 

 in effect, an interrupted current, and it is sometimes 

 spoken of as if it really consisted of an alternation of 

 currents which move first in one direction and then in 

 another. Such a conception is not really justifiable. 

 The more plausible explanation is that the alternating 

 current is one in which the electrons are not evenly dis- 

 tributed and move with irregular motion. Perhaps we 

 may think of the individual electrons of such a current as 



[196] 



