406 THE ADDRESSES, LECTURES, ETC., OF 



to a dynamo-electrical machine, a very powerful electrical current 

 will be the result, which may be carried to a great distance, 

 through a large metallic conductor, and then be made to impart 

 motion to electro-magnetic engines, to ignite the carbon points of 

 electric lamps, or to effect the separation of metals from their 

 combinations. A copper rod ( 3 inches in diameter would be 

 capable of transmitting 1,000 HP. a distance of say 30 miles, an 

 amount sufficient to supply one quarter of a million candle-power, 

 which would suffice to illuminate a moderately-sized town." This 

 suggestion was much criticised at the time, when it was still 

 thought that electricity was incapable of being massed so as to 

 deal with many horse -power of effect, and the size of conductor I 

 proposed was also considered wholly inadequate. It will be inte- 

 resting to test this early calculation by recent experience. Mr. 

 Marcel Deprez has, it is well known, lately succeeded in trans- 

 mitting as much as 3 HP. to distances up to 40 kilometers 

 (25 miles) through a pair of ordinary telegraph wires of 4 milli- 

 metres diameter. The results so obtained were carefully noted by 

 Mr. Tresca, and were communicated a fortnight ago to the French 

 Academy of Sciences. Taking the relative conductivity of the 

 iron wire employed by Deprez, and the 3-inch rod proposed by 

 myself, the amount of power that could be transmitted through 

 the latter would be about 4,000 HP. But Deprez employed a 

 motor-dynamo of 2,000 Volts, and was contented with a yield of 

 32 per cent, only of the power imparted to the primary machine, 

 whereas I calculated at the time upon an electromotive force of 

 200 Volts, and upon a return of at least 40 per cent, of the energy 

 imparted. Sir William Thomson at once accepted these sugges- 

 tions, and with the conceptive ingenuity peculiar to himself, went 

 far beyond me, in showing before the Parliamentary Electric 

 Light Committee of 1879, that through a copper wire of only 

 |-inch diameter, 21,000 HP. might be conveyed to a distance of 

 300 miles with a current of an intensity of 80,000 Volts. The 

 time may come when such a current can be dealt with, having a 

 striking distance of about T2 foot in air, but then, probably, a 

 very practical law enunciated by Sir William Thomson would be 

 infringed. This is to the effect that electricity is conveyed at the 

 cheapest rate through a conductor, the cost of which is such that 

 the annual interest upon the money expended equals the annual 



