S/K WILLIAM SIEMENS, F.R.S. 405 



dynamo-machine has only one moving part well balanced, and is 

 acted upon along its entire circumference by propelling force. 

 Jacobi proved, many years ago, that the maximum efficiency of a 



magneto-electric engine was obtained when ~ = = _ which law 



has been construed, by Verdet (The'orie Me"canique de la 

 Chaleur) and others, to mean that one-half is the maximum 

 theoretical efficiency obtainable in electric transmission of power, 

 and that one-half of the current must be necessarily wasted or 

 turned into heat. I could never be reconciled to a law neces- 

 sitating such a waste of energy, and have maintained, without 

 disputing the accuracy of Jacobi's law, that it has reference really 

 to the condition of maximum work accomplished with a given 

 machine, whereas its efficiency must be governed by the equation 



A Jt) 



g = -Ty- = nearly 1. From this it follows that the maximum yield 



is obtained when two dynamo-machines (of similar construction) 

 rotate nearly at the same speed, but under these conditions the 

 amount of force transmitted is a minimum. Practically the best 

 condition of working consists in giving to the primary machine 

 such proportions as to produce a current of the same magnitude, 

 but of 50 per cent, greater electromotive force than the secondary ; 

 by adopting such an arrangement, as much as 50 per cent, of the 

 power imparted to the primary could be practically received from 

 the secondary machine at a distance of several miles. Professor 

 Silvanus Thompson, in his recent Cantor Lectures, has shown an 

 ingenious graphical method of proving these important funda- 

 mental laws. 



The possibility of transmitting power electrically is so obvious 

 that suggestions to that effect have been frequently made since 

 the days of Volta, by Ritchie, Jacobi, Henry, Page, Hjorth and 

 others ; but it is only in recent years that such transmission has 

 been rendered practically feasible. 



Just six years ago, when delivering my presidential address to 

 the Iron and Steel Institute, I ventured to suggest that "time 

 will probably reveal to us effectual means of carrying power to 

 great distances, but I cannot refrain from alluding to one which 

 is, in my opinion, worthy of consideration, namely, the electrical 

 conductor. Suppose water-power to be employed to give motion 



