THE AVAILABLE ENERGY OF NATURE. 93 



for power, as they grow beside navigable rivers, for shipping. Thus, 

 hitherto, the use of water-power has been confined chiefly to isolated 

 factories which can be conveniently placed and economically worked 

 in the neighborhood of natural waterfalls. But the splendid sugges- 

 tion made about three years ago by Mr. Siemens in his presidential 

 address to the Institution of Mechanical Engineers, that the power of 

 Niagara might be utilized, by transmitting it electrically to great dis- 

 tances, has given quite a fresh departure for design in respect to econo- 

 my of rain-power. From the time of Joule's experimental electro-mag- 

 netic engines developing ninety per cent, of the energy of a voltaic 

 battery in the form of weights raised, and the theory of the electro- 

 magnetic transmission of energy completed thirty years ago on the 

 foundation afforded by the train of experimental and theoretical inves- 

 tigations by which he established his dynamical equivalent of heat in 

 mechanical, electric, electro-chemical, chemical, electro-magnetic, and 

 thermo-elastic phenomena, it had been known that potential energy 

 from any available source can be transmitted electro-magnetically by 

 means of an electric current through a wire, and directed to raise 

 weights at a distance, with unlimitedly perfect economy. The first 

 large-scale practical application of electro-magnetic machines was pro- 

 posed by Holmes in 1854, to produce the electric light for lighthouses, 

 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 

 invention, 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 independ- 

 ently, and as nearly as may be simultaneously, in 1867 by Dr. Werner 

 Siemens, Mr. S. A. Varley,'and Sir Charles Wheatstone a discovery 

 which constitutes an electro-magnetic analogue to the fundamental 

 electrostatic principle of Nicholson's revolving doubler, resuscitated 

 by Mr. C. F. Varley in his instrument "for generating electricity," 

 patented in 1860 ; and by Holtz in his celebrated electric machine ; 

 and by myself in my "replenisher " for multiplying and maintaining 

 charges in Leyden jars for heterostatic electrometers, and in the elec- 

 trifier for the siphon of my recorder for submarine cables. 



The dynamos of Gramme and Siemens, invented and made in the 

 course of these fourteen years since the discovery of the fundamental 

 principle, give now a ready means of realizing economically on a large 

 scale for many important practical applications the old thermo-dy- 

 namics of Joule in electro-magnetism ; and, what particularly concerns 

 us now in connection with my present subject, they make it possible 

 to transmit electro-magnetically the work of waterfalls through long, 

 insulated conducting wires, and use it at distances of fifties or hun- 



