ELECTRIC LIGHTING. 305 



burning of the Jablochkoff candle. By using a machine 

 which produces alternating currents, M. Jablochkoff obviates 

 this difficulty, the carbons being alternately positive and 

 negative (in extremely rapid succession), and therefore con- 

 suming at the same rate. 



The Jablochkoff candle lasts only about an hour and a 

 half. But four, six, or more candles may be used in the 

 same globe or lantern, and automatic arrangements adopted 

 to cause a fresh candle to be ignited at the moment when 

 its predecessor is burnt out. 



In Paris and elsewhere (as in Holborn, for instance), 

 each Jablochkoff lamp is enclosed in an opal glass globe. 

 Mr. Hepworth remarks on this, that in his opinion the use 

 of the opal globe is a mistake, as it shuts off quite 50 per 

 cent, of the light without any corresponding advantage, 

 except the correction of the glare. ' This wasteful dis- 

 advantage will no doubt be remedied in the future/ he says, 

 by the use of some less dense medium. ' Mr. Shoolbred 

 states that from a series of careful photometric experiments 

 carried out by the municipal authorities with the Jablochkoff 

 lights, each naked light is found to possess a maximum 

 intensity of 300 candles. With the opal globe this was 

 reduced to 180 candles, showing a loss of 40 per cent., 

 while during the darker periods through which the light 

 passed the light was as low as 90 candles. It may be men- 

 tioned here that Mr. Van der Weyde, who has long used 

 the electric light for photographic purposes, has given much 

 attention to the important problem of rendering the electric 

 light available as an illuminator without wasting it, and yet 

 without throwing the rays directly upon the object to be 

 illuminated. The rays are intercepted by an opal disc 

 about four inches in diameter, and the whole body of the 

 rays is gathered up by a concave reflector (lined with a white 

 material), and thrown out in a flood of pure white light, in 

 which the most delicate shades of tint are discernible. He 

 can use any form of electric candle in this way. Only it 

 should be noticed, before the employment of his method is 



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