680 FRAGMENTS OF SCIENCE. 



piece is immediately dissipated or removed by the current, 

 the passage of which once established is afterward main- 

 tained. The carbons gradually waste, while the substance 

 between them melts like the wax of a candle. The com- 

 parison, however, only holds good for the act of melting; 

 for, as regards the current, the insulating plaster is practi- 

 cally inert. Indeed, as proved by M. Rapieff and Mr. 

 Wilde, the plaster may be dispensed with altogether, the 

 current passing from point to point between the naked 

 carbons. M. de Meritens has recently brought out anew 

 candle, in which the plaster is abandoned, while between 

 the two principal carbons is placed a third insulated rod of 

 the same material. With the small de Meritens machine 

 two of these candles can be lighted before you; they 

 produce a very brilliant light. * In the Jablochkoif candle 

 it is necessary that the carbons should be consumed at the 

 same rate. Hence the necessity for alternating currents 

 by which this equal consumption is secured. It will be 

 seen that M. Jablochkoff has abolished regulators 

 altogether, introducing the candle principle in their 

 stead. In my judgment, the performance of the Jabloch- 

 koff candle on the Thames Embankment and the Holborn 

 Viaduct is highly creditable, notwithstanding a consider- 

 able waste of light toward the sky. The Jablochkoif lamps, 

 it may be added, would be more effective in a street, where 

 their light would be scattered abroad by the adjacent 

 houses, than in the positions which they now occupy in 

 London. 



It was my custom some years ago, whenever I needed a 

 new and complicated instrument, to sit down beside its 

 proposed constructor, and to talk the matter over with 

 him. The study of the inventor's mind which this habit 

 opened out was always of the highest interest to me. I 

 particularly well remember the impression made upon me 

 on such occasions by the late Mr. Darker, a philosophical 

 instrument maker in Lambeth. This man's life was a 

 struggle, and the reason of it was not far to seek. No 

 matter how commercially lucrative the work upon which 



* The machine of M. de Meritens and the Farmer- Wallace machine 

 were worked by an excellent gas-engine, lent for the occasion by the 

 Messrs. Croysley, of Manchester. The Siemens machine was worked 

 by steam. 



