ELECTRIC AND GAS ILLUMINATION. 581 



rent sufficient to maintain from sixteen thousand to eighteen thousand 

 sixteen-candle lamps. Taking the former figure, this is one and a 

 quarter mile per 1,000 lamps. Basing the calculation for mains upon 

 this mileage and the size of the present mains, the same number of 

 miles of electric mains would be required as for gas. The present 

 conductors are, as stated, in the form of half-round copper rods, of 

 varying sizes, diminishing of course as they proceed from the station. 

 They are, however, equivalent to round rods with a uniform diameter 

 of one half inch. Such rods weigh A y o *j of a pound per foot, and 

 3986*4 pounds per mile, costing, at 28 cents per pound, 81,116 per 

 mile. As there are two rods in each main, the cost per mile for 

 copper would be $2,232. To this must be added $1,200 per mile for 

 wrouo-ht-iron tube, boxes at the joints between the mains and house- 

 wires, and insulating material, and $1,000 per mile for laying, making 

 the total cost of the main per mile, laid ready for use, $4,432. Four 

 fifths of the mains would be of this size, the other fifth being feeders 

 equivalent to round rods three fourths of an inch in diameter. These 

 latter weigh T69 pound per foot, and would therefore cost $2,340 

 per mile, and, taking the cost of inclosing tube, insulation, and laying 

 the same as above, their total cost per mile would be $7,196. The 

 total cost of the mains, forty miles at $4,432 per mile, and ten miles 

 at $7,196 per mile, would therefore amount to the same as the gas- 

 mains, viz., $250,000. If real estate be added at $50,000, which in 

 most cities requiring this size of plant would be ample, the total cost 

 of the electric plant would be the same as one for gas.* 



The elements entering into the cost of the light to the company 

 furnishing it are, in each case, the interest on the investment, depre- 

 ciation, or the amount spent each year in keeping the property in good 

 condition, the labor of all kinds in the manufacture, distribution, and 

 management and lastly the cost of the materials used in its produc- 

 tion. In the case of gas but a few of these items as they occur in 

 American works are obtainable, so that recourse must be had to the 

 published reports of foreign companies, and the like items estimated 

 for this country. Of these, the reports of the London companies as 

 analyzed by Mr. Field will best serve for the purpose of the present 

 comparison.f Taking first the item of depreciation, we find that for 

 the four metropolitan companies this was, for the year 1880, on the 

 producing portion of the plant 9*86 cents per 1,000 feet of gas sold, 

 or about five and a half per cent on the cost of this part of the plant 

 as it^ has been taken in this paper. Calling this ten cents a thousand 



* "WTiile this estimate seems to me not far from the expenditure that would be actually 

 required for this size of plant, it should be stated that it is lower than any of those given 

 by the electrical experts examined by the select committee of the House of Commons in 

 its consideration of the Electric Lighting Bill. 



f Having been unable to obtain a copy of 3Ir. Field's " Annual," I have taken the 

 figures as quoted from this for the year 1SS0 by Mr. Dowson, in a recent lecture before 

 the Society of Arts. 



