TRANSACTIONS OF SECTION A. 517 



dynamical equivalent of heat in mechanical, electric, electro-chemical, chemical, 

 electro-magnetic, and thermoclastic 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 v^ire, and directed to raise weights at a distance, 

 with unlimitedly perfect economy. The first large-scale practical application of 

 electro-magnetic machines was proposed by Holmes in 1854, to produce the elec- 

 tric 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 Fore- 

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

 Siemens, Mr. S. A. Varley, and Sir Charles Wheatstone ; a discovery which con- 

 stitutes an electro-magne'tic 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 main- 

 taining charges in Leyden jars for heterostatic electrometers, and in the electri- 

 fier 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 realising economically on a large scale, for many important practical 

 applications, the old thermo-dynamics 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 in- 

 sulated conducting wires, and use it at distances of fifties or hundreds of miles 

 from the source, ^vith excellent economy — better economy, indeed, in respect to 

 proportion of energy used to energy dissipated than almost anything known in 

 ordinary mechanics" and hydraulics for distances of hundreds of yards instead of 

 hundreds of miles. 



In answer to questions put to me in May, 1879,^ by the Parliamentary Com- 

 mittee on Electric Lighting, I gave a formula for calculating theamount of energy 

 transmitted, and the amount dissipated by being converted into heat on the 

 way, through an insulated copper conductor of any length, with any given 

 electro-motive force applied to produce the current. Taking Niagara as ex- 

 ample, and with the idea of bringing its energy usefully to Montreal, Boston, 

 New York, and Philadelphia, I calculated the formula for a distance of 300 

 British statute miles (which is greater than the distance of any of those four 

 cities trom Niagara, and is the radius of a circle covering a large and very 

 important part of the United States and British North America ), and found almost 

 to my surprise that, even with so great a distance to be provided for, the con- 

 ditions are thoroughly practicable with good economy, all aspects of the case 

 carefully considered. The formula itself will be the subject of a technical com- 

 munication to Section A in the course of the Meeting on which we are now enter- 

 ing. I therefore at present restrict myself to a slight statement of results. 



1. Apply dynamos driven by Niagara to produce a difference of potential of 

 80,000 volts between a gnod earth-connection and the near end of a solid copper 

 wire of half an inch (1-27 centimetre) diameter, and 300 statute miles (483 kilo- 

 metres) length. . . 1. 



2. Let resistance by driven dynamos doing work, or by electric lights, or, as I 

 can now say, by a Faure battery taking in a charge, be applied to keep the remote 

 end at a potential differing by 64,000 volts from a good earth-plate there. 



3. The result will be a current of 240 webers through the wire taking energy 

 from the Niagara end at the rate of 26,250 horse-power, losing 5,250 (or 20 per 



' Printed in the Parliamentary Blue Book Keport of the Committee on Electric 

 Lighting, 1879. 



