94 THE POPULAR SCIENCE MONTHLY. 



dreds 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 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 Parlia- 

 mentary Committee on Electric Lighting, I gave a formula for cal- 

 culating 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 electromotive force applied 

 to produce the current. Taking Niagara as example, 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 Brit- 

 ish 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 Amer- 

 ica), 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 difference 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 centimetres) 

 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 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 twenty per cent.) of this by the generation and dis- 

 sipation of heat through the conductor and 21,000 horse-power (or 

 eighty 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 differ- 

 ence of potentials of 80,000 volts (or 5,000 DanielPs) is (Thomson's 

 "Electrostatics and Magnetism," 340) only eighteen millimetres, 

 and therefore there is no difficulty about the insulation. 



* Printed in the " Parliamentary Bluc-Book Reports of the Committee on Electric 

 Lighting," 1879. 



