22 Electricity as an Illuminant. 



hours of lighting were only 225 per annum, the interest for 

 each hour would be double compared to that for the 450 hour 

 calculation. Take a test case of a factory requiring 500 lights 

 of 16 candle-power,and we will assume that there is sufficient 

 margin of engine power to drive the dynamo, which of course 

 is favourable to the comparative cost of electric light to that of 

 gas. On the other hand, electric light installations are generally 

 handicapped as against gas if the latter is already in operation, 

 because the interest on the electric light plant is debited to 

 it, whereas no interest is charged to the gas fittings after they 

 have been erected. With new buildings the case is different. 

 The lecturer proceeded to give a number of figures and details 

 with reference to the proportionate cost. His conclusion was 

 that 500 electric incandescent lights used for 450 hours a year 

 in a mill or works where spare engine power can be used for 

 driving the dynamos will cost ;^I44 17s. 6d. If the arc light 

 can be used — as it can in the case of factories or shops having 

 high ceilings and large space — the cost will not be more than 

 half that amount. The cost of 500 gas lights — basing the 

 calculation on an expenditure of six cubic feet per hour for each 

 lamp, and on the price of gas at 2s. yd. per thousand feet, would 

 be for the same amount of time — 450 hours per year — 

 £t.*]^ 7s. 6d., and adding £Z for incidental expenses, such as 

 renewal of burners, &c., would bring it up to £\'i2 7s. 6d. 

 Where hghts are used for a shorter time, however, the case is 

 very different, and the result comes out most unfavourably for 

 the electric light. Take 350 hours a year, for instance, in a 

 shop or other place where special power has to be supplied to 

 drive the dynamo, the cost will be some ^220 12s. And if the 

 supply is taken from a central station the figures are still more 

 startling, for, taking it at 6d. per Board of Trade unit — it is 

 contemplated, I believe, to charge yd. in Belfast — the cost for 

 the current alone for these lamps will be _;^ 284 7s. bd., and other 

 expenses will bring the total cost up to £z^<i 7s. 6d., as against 

 ^220 I2s. where the consumer puts in his own plant for driving 

 the dynamo. The cost of gas under similar circumstances will 

 be only;^i65 12s. 6d. 



