SCIENCE. 



477 



is taken from a town supply are generally very small, such 

 as working the bellows of an organ, or "hair-brushing by 

 machinery," and involve simply throwing away the used 

 water. The cost of energy thus obtained must be some- 

 thing enormous in proportion to the actual quantity of 

 the energy, and it is only the smallness of the quantity 

 that allows the convenience of having it when wanted at 

 any moment, to be so dearly bought. 



For anything of great work by rain-power, the water- 

 wheels must be in the place where the water supply with 

 natural fall is found. Such places are generally far from 

 great towns, and the time is not yet come when great 

 towns grow by natural selection beside waterfalls 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 suggestion 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 distances, has given quite a fresh 

 departure for design in respect to economy of rain-power. 

 From the time of Joule's experimental electro-magnetic 

 engines developing 90 percent 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 investigations by which he 

 established his dynamical equivalent of heat in mechan- 

 ical, electric, electro-chemical, chemical, electro-magnetic, 

 and thermoclastic phenomena, it had been known that 

 potential energy from any available source can be trans- 

 mitted electro-magnetically by means of an electric cur- 

 rent 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 proposed by Holmes in 1854, to produce 

 the electric hght for lighthouses, and persevered in by 

 him till he proved the availibility of his machine to the 

 satisfaction of the Trinity House and the delight of Far- 

 aday in trials at Blackwall in April, 1857, and it was ap- 

 plied to light the South Foreland lighthouse on Decem- 

 ber 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 engi- 

 neering, 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 Sie- 

 mens, 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 

 i860; and by Holtz in his celebrated electric machine ; 

 and by myself in my " replenisher " for multiplying and 

 maintaining charges in Leyden jars for heterostatic elec- 

 trometers, and in the electnfier for the siphon of my re- 

 corder for submarine cables. 



The dynamos of Gramme and Siemens, invented and 

 made in the course of these fourteen years since the dis- 

 covery of the fundamental principle, give now a ready 

 means of realizing 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 insulated conducting 

 wires/and use it at distances of fifties or hundreds of 

 miles from the source, with excellent economy — better 

 economy, indeed, in respect to proportion of energy used 

 to energy dissipated than almost anything known in ordi- 

 nary 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 Committee on Electric Lighting, I gave a 

 formula for calculating the amount 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 pro- 

 duce the current. Taking Niagara as example, and with 

 the idea of bringing its energy usefully to Montreal, Bos- 

 ton, New York, and Philadelphia, I calculated the formula 

 for the distance of 300 British statute miles (which is 

 greater than the distance of any of those four cities from 

 Niagara, and is the radius of a circle covering a large and 

 very important part of the United States and British North 

 America), I found almost to my surprise that, even with 

 so great a distance to be provided for, the conditions are 

 thoroughly practicable with good economy, all aspects of 

 the case carefully considered. The formula itself will be 

 the subject of a technical communication to Section A in 

 the course of the meeting on which we are now entering. 

 I therefore at present restrict myself to a slight statement 

 of results. 



1. Apply dynamos driven by Niagara to produce a dif- 

 ference of potential of 80,000 volts between a good earth 

 connection and the near end of a solid copper wire of half 

 an inch (1.27 centimetre) diameter, and 300 statute miles 

 (483 kilometres) length. 



2. Let resistance by driven dynamos doing work, or 

 by electric lights, or, as I can now say, by a Faure bat- 

 tery 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 5250 (or 20 per cent) of 

 this by the generation and dissipation of heat through the 

 conductor and 21,000 horse-power (or 80 per cent of the 

 whole) on the recipients at the far end. 



4. The elevation of temperature above the surrounding 

 atmosphere, to allow the heat generated in it to escape by 

 radiation and be carried away by convection is only about 

 20 Centigrade ; the wire being hung freely exposed to air 

 like an ordinary telegraph wire supported on posts. 



5. The striking distance between flat metallic surfaces 

 with difference of potentials of 80,000 volts (or 75,000 

 Daniell's) is (Thomson's " Electrostatics and Magnetism." 

 § 340) only 18 millimetres, and therefore there is no diffi- 

 culty about the insulation. 



6. The cost of the copper wire, reckoned at 8d. per [b., 

 is ^37,000, the interest on which at 5 per cent is ^1900 a 

 year, If 5250 horse-power at the Niagara end costs more 

 than ^1900 a year, it would be better economy to put more 

 copper into the conductor ; if less, less. I say no more 

 on this point at present, as the economy of copper for 

 electric conduction will be the subject of a special com- 

 munication to the Section. 



I shall only say, in conclusion, that one great difficulty 

 in the way of economizing the electrical transmitting 

 power to great distances, or even to moderate distances 

 of a few kiloms., is now overcome by Faure's splendid in- 

 vention. High potential — as Siemen s, I believe, first 

 pointed out — is the essential for good dynamical economy 

 in the electric transmission of power. But what are we 

 to do with 80,000 volts when we have them at the civilized 

 end of the wire? Imagine a domestic servant going to 

 dust an electric lamp with 80,000 volts on one of its metals? 

 Nothing above 200 volts ought on any account ever to be 

 admitted into a house or ship or other place where safe- 

 guard against accident cannot be made absolutely and 

 forever trustworthy against all possibility of accident. 

 In an electric workshop 80,00c volts is np more dangerous 

 than a circular saw. Till I learned Faure's invention I 

 could but think of step-down dynamos, at a main receiv- 

 ing station to take energy direct from the electic main 



* Printed in the Parliamentary Blue-book Report of the Committee on 

 Electric Lighting, 1879. 



