MAN'S CO-LABORER: THE DYNAMO 



to excite the field magnet, while the main current as 

 given off by the rest of the coils was taken off by ring- 

 contacts, the machine being a self-exciting, alternating- 

 current dynamo. 



The Italian, Picnotti, in 1864 invented a ring arma- 

 ture which, although provided with teeth was wound 

 with coils in such a way as to obtain a very uniform 

 current; but the practical introduction of the con- 

 tinuous-current machines dates from 1870, when 

 Gramme re-invented the ring and gave it the form 

 which is still in vogue. Von Alteneck in 1873 con- 

 verted the Siemens shuttle armature along the same 

 lines and so introduced the drum arrangement which 

 has since been very extensively adopted. 



Thus through the efforts of a great number of workers 

 the idea of utilizing electromagnetic energy for the 

 purposes of the practical worker came to be a reality. 

 Numberless machines have been made differing only as 

 to details that need not detain us here. Everyone is 

 familiar with sundry applications of the dynamo to the 

 purposes of to-day's applied science. It must be under- 

 stood, of course, that the amount of electricity generated 

 in any dynamo is precisely measurable, and that by 

 no possibility could the energy thus developed exceed 

 the energy required to move the coils of wire. Were 

 it otherwise the great law of the conservation of energy 

 would be overthrown. In actual practice, of course, 

 there is loss of energy in the transaction. The current 

 of electricity that flows from the very best dynamo repre- 

 sents considerably less working power than is expended 

 by the steam engine in forcibly revolving the armature. 



