and Transmission of Power. 29 



be submitted to in the employment of the "incandescent" light. 

 As a rule, one actual horse-power will give from 1,500 to 1,800 

 candle power by arc lighting, or from 160 to 180 candles by 

 incandescent lamps. Another system of lamp, somewhat be- 

 tween the arc and the incandescent, is what has been termed 

 " semi-incandescent." It consists of a thin rod of carbon which 

 is caused to press against a heavy block of the same or other 

 material, and the light is emitted where the two unite ; but 

 this method has not been much employed. 



The method in which an installation of arc lighting is carried 

 out is quite different from that which has to be adopted for 

 incandescent. In the former, the lamps are arranged in " series," 

 that is, the current is driven through the first lamp, then 

 through the second, and so on, finally returning to the machine. 

 The quantity of electricity required is always the same whether 

 one or forty lamps are used, but the potential ox pressure of the 

 current has to be increased for every lamp. With incandescent 

 lighting, a portion of the current is sent through each lamp 

 independently of its neighbour. The cables are arranged in 

 parallels, very similar to the sides of a step-ladder, and the 

 incandescent lamps are attached between them, thus being 

 analogous to the steps of the ladder. It is obvious by this 

 arrangement that the pressure or potential of the current should 

 remain constant, but the quantity should be in proportion to the 

 number of lamps, ten lamps requiring ten times as much current 

 as one lamp. 



Now, as regards the danger of fire in connection with electric 

 lighting, there is no artificial mode of illumination so safe if 

 properly installed, and none so dangerous if erected in ignorance 

 of what is necessary. The danger arises from what I may term 

 the insidious nature of the current. If there is a leak in a gas 

 pipe, it can generally be detected without .the reprehensible 

 method of trying for it with a light, but there may be a condition 

 of affairs with an improperly erected installation of the electric 

 light which will give no warning before damage is done. For 

 instance, cables may be dangerously near to iron without being 

 properly protected; in course of time they may come into metallic 



