.$//? WILLIAM SIEMENS, F.K.S. 375 



This, then, is the principle on which the size of a conductor should 

 !K- determined. 



From the experience of large installations, I consider that 

 electricity can, roughly speaking, be produced in London at a cost 

 of about one shilling per 10,000 Ampdre-Volts or Watts (746 

 Watts being equal to 1-horse power) for an hour. Hence, assuming 

 that each set of four incandescence lamps in series (such as Swan's, 

 but for which may be substituted a smaller number of higher re- 

 sistance and higher luminosity) requires 200 volts electromotive 

 force, and 60 Watts for their efficient working, the total current 

 required for 64,000 such lights is 19,200 amperes, and the cost of 

 the electric energy lost by this current in passing through T^Q th of 

 an ohm resistance, is 16 per hour. 



The resistance of a copper bar one quarter of a mile in 

 length, and one square inch in section, is very nearly r^th of an 

 ohm, and the weight is about 2^ tons. Assuming, then, the price 

 of insulated copper conductor at 90 per ton, and the rate of 

 interest and depreciation at 1\ per cent., the charge per hour of 

 the above conductor, when used eight hours per day, is \\d. 

 Hence, following the principle I have stated above, the proper size 

 of conductor to use for an installation of the magnitude I have 

 supposed, would be one of 48'29 inches section, or a round rod 

 eight inches diameter. 



If the mean distance of the lamps from the station be assumed 

 as 850 yards, the weight of copper used in the complete system of 

 conductors would be nearly 168 tons, and its cost 15,120. To 

 this must be added the cost of iron pipes, for carrying the con- 

 ductors underground, and of testing boxes, and labour in placing 

 them. Four pipes of 10-inch diameter each, would have to proceed 

 in different directions from the central station, each containing 

 sixteen separate conductors of one inch diameter, and separately 

 insulated, each of them supplying a sub-district of 1,000 lights. 



The total cost of establishing these conductors may be taken at 

 37,000, which brings up the total expenditure for central station 

 and leads to 177,000. I assume the conductors to be placed 

 underground, as I consider it quite inadmissible, both as regards 

 permanency and public safety and convenience, to place them 

 above ground, within the precincts of towns. With this expendi- 

 ture, the parish of St. James's could be supplied with the electric 



