RKYIKXY OF LIGHTING SYSTKMS. 105 



scale of depreciation would lead us to expect ; and if we allow 5 per cent, interest on capital for the 

 acetylene plant, it should also he allowed on the lamps and candlesticks. Furthermore, the servants time 

 in attending to the generator should he considerably less than that required for lamp trimming. 



The foregoing view has been set out at some length, as it seems that in the case ol small private 

 plants the cost of running is made to appear unduly high by the addition of fixed percentages on capital 

 outlay to running costs. Let us consider the first cost of the plant for supplying 50, 100 and 150 lights. 

 A manufacturer who supplies all three systems, and may therefore be trusted not to enlarge unduly on the 

 merits of any particular one of them, gives the iollowing as the cost of such installations complete from 

 the generator to the lights : 



.Yd. o/ lights. lUectricily. Air-gns. Acetylene. 



50 . . (i ;o . . 105 . . /J,X ; 



loo . . 205 . . 200 . . 150 



150 .. 275 .. 250 .. 217 



These figures are only approximate, and would vary according to the circumstances in which the 

 installation was to he carried out ; furthermore, in studying the comparisons of this table it should be 

 remembered that the costs given in each class are for one type of plant only. There are more cosily forms 

 on the market which have certain advantages. This is more particularly the case with the acetylene 

 system. 



Our next consideration is the cost of the fuel necessaiy to keep these plants at work, and in this 

 we may take as a convenient standard the cost of the fuel required to run a do candle-power light toi 

 1,000 hours. In the case of electricity \ve assume the use of ordinary paraffin oil at (id. per gallon. The 

 manufacture of air-gas requires the use of petrol, and it should he remembered that the Government 

 duty can be reclaimed on petrol that is not used for driving motor-cars, so we may take the price a-; is. 

 per gallon. Calcium carbide lor the manufacture of acetylene costs 12 los. per ton. Now, an oil engine 

 for driving a dynamo of about the si/.e we are considering would require about one pint of paraffin per 

 horse-power per hour, but we can only reckon on three-quarters of a horse-power being available at the 

 lamps, as we must. allow lor losses in the dynamo and accumulators. A oo candle-power metallic tilament 

 lamp taking n watts per candle-power would require (&amp;gt;(&amp;gt; Hoard of Trade units to keep it running foi 

 1,000 hours. As a horse-power for one, hour is equivalent to o 7-jd Hoard of Trade units, this is equivalent 

 to SiS 5 horse-power hours. Xow, we have seen that we can get three-quarters of a horse-power at the 

 lamps for one hour at the cost ol one pint of paraffin, so it follows that we should use ^N\5 : : , ! 117. , pints 

 to keep a 60 candle-power lamp going ior 1,000 hours ; this works out to /s. -jd. with paraffin at (&amp;gt;d. per 

 gallon. 



In the case of air-gas careful experiments have shown that a Oo candle-power light can lie kept 

 going for fifteen hours at the cost of id., assuming the cost of petrol at is. per gallon. This means thai 

 the same light for 1,000 M5 MrO pence, or about 5*. old. A 60 candle-power open flame acetylene 

 burner consumes about I. , cubic feet of the gas per hour, and good calcium carbide at 12 IDS. per ton 

 will produce 5 cubic feet of acetylene to the pound weight. YVe therefore require 1.51)0 cubic feet to keep 

 the burner going for 1,000 hours, that is, 1,500-^5^300111. of carbide ; the cost of this at. say. i|d. per 

 pound works out to 1 us. }d. This latter would appear to be a very high figure when compared with 

 the other two, but as will be seen from what follows, tliere are many circumstances which tend to modify 

 the position when the question becomes the practical one of lighting a house and not a purely academic 

 comparison of fuel against candle-power per hour. Xow, it will be observed that the air-gas in this 

 comparison is the cheapest, and in cases where a house is required to be lit throughout by 60 candle-power 

 lights it undoubtedly is so ; but whereas electricity and acetylene can be used in lights of smaller candle- 

 power, thus allowing economies to be made in passages, lobbies, etc., the smallest burner that can be 

 successfully used with air-gas gives 40 to 60 candle-power. Acetylene has the additional advantage that 

 it can be turned down when not required. This, of course, cannot be done with any form of gas lighting 

 that makes use of an incandescent mantle, and the dimming of the electric light is rather a 

 wasteful proceeding, save in cases where the alternate current system is used. In all but very exceptional 

 instances country house plants are designed to give continuous currents, when the use of dimmers is 

 distinctly uneconomical. 



In the above comparison table of first costs the lights are not of equal candle-power ; for the 

 electric system they are assumed to be a proportion of 12, 16 and 20 candle-power, for the air-gas they would 

 all be 60 candle-power and for the acetylene they would all be 22 candle-power. This seems to be the 

 fairest way of making the comparison, as it is not a question of obtaining the greatest candle-power at 

 the least cost, but of efficiently lighting a house, and a system which can give a small light where only 

 such is required should be able to claim this advantage. The amount of attention required to operate 

 an air-gas or acetylene plant is very small, and it is not unusual to make it part of the housemaid s duty. 

 In the case of electric light the writer has never heard of this having been done ; male attention of some 

 sort appears to be required, even if it is only such as the bootboy can give. Gardeners can usually 



