SOURCES OF MECHANICAL EFFECT. 449 



The first large-scale practical application of elec- 

 ^tro-magnetic machines was proposed by Holmes 

 in 1854, to produce the electric light for light- 

 houses, and persevered in by him till he proved 

 the availability of his machine to the satisfaction 

 of the Trinity House and the delight of Faraday 

 in trials at Blackwall in April, 1857, and it was 

 applied to light the South Foreland lighthouse on 

 December 8, 1858. This gave the impulse to in- 

 vention ; by which the electro-magnetic machine 

 has been brought from the physical laboratory into 

 the province of engineering, and has sent back to 

 the realm of pure science a beautiful discovery 

 that of the fundamental principle of the dynamo, 

 made triply and independently, and as nearly as 

 may be simultaneously, in 1867 by Dr. Werner 

 Siemens, Mr. S. A. Varley, and Sir Charles Wheat- 

 stone ; a discovery which constitutes an electro- 

 magnetic analogue to the fundamental electrostatic 

 principle of Nicholson's revolving doubler, resus- 

 citated by Mr. C. F. Varley in his instrument " for 

 generating electricity"; patented in 1860; and 

 by Holtz in his celebrated electric machine ; and 

 VOL. II G G 



