Electricity as an Illuminant. 21 



again transformed down to 75 volts, and used for lighting and 

 motor purposes. Alternating current motors are quite feasible, 

 but they do not appear to be so simple to start as those for 

 direct currents. A noteworthy feature of the Frankfort- 

 LaufFen current is the employment of the three wires, each 

 conveying three separate alternating currents flowing in separate 

 phases, following each other like a current of water actuated by 

 a three-plunger pump. This method seems to overcome the 

 defects of alternating motors, and it is said to prevent any dis- 

 turbance by induction to contiguous telephone or telegraph 

 wires. It also reduces the danger inherent in all high-pressure 

 currents, more especially of the alternating or intermittent 

 kind. Possibly without going very exhaustively into the 

 respective merits of the various central supply systems, I may 

 be allowed to give my opinion that for Belfast probably the 

 direct current is preferable. For arc lighting it is unquestion- 

 ably the best. A great advantage it possesses is that it provides 

 for the use of storage batteries, which are a reserve in case of 

 emergency, and these can be charged up during the day, when 

 the lighting load is not heavy. 



With reference to the comparative cost of electric light and 

 gas, it has been often said that figures may be made to prove 

 anything. To the general question whether or not the electric 

 light is cheaper than gas, my answer is that under special 

 conditions it is cheaper and under other conditions it is dearer. 

 The conditions which are advantageous to the electric light are 

 wide spaces with high ceilings, in which arc lights can be em- 

 ployed. The longer the hours per annum in which the light 

 has to be kept in operation, the more advantageous for elec- 

 tricity. This arises from the fact that one of the most serious 

 items in connection with electric light installation is the interest 

 and depreciation allowance on the first cost. T always reckon 

 these as amounting to 9 per cent., viz., 5 per cent, for interest 

 and 4 per cent, for depreciation. The average hours for mill or 

 workshop lighting are about 450 per annum, hence the 9 per 

 cent, must be debited to these hours. It is manifest that if the 



