practice where the Electric Light is pennanenth' employed. When 

 a cuiTent of electricity meets with resistance to its passage, heat is 

 generated, and, if the temperature be sufficiently raised, light also is 

 given out, but the resistance must be localized so as to concentrate 

 the heat over a small area. The two plans adopted to obtain the 

 necessary resistance, viz., — the one, by separating the conducting 

 carbon rods by a small air space (the "voltaic arc" method) ; and the 

 other by interposing a short length of highly resisting substance, 

 such as platinum or carbon of small diameter (the "incandescent" 

 method) were described and illustrated. As examples of the voltaic 

 arc arrangement the Duboscq and Wallace-Farmer lamps, and the 

 Jablochkoff and Wilde caridles. and as examples of the combination 

 of arc and incandescence, the Werdenaiann and Ecjaiier lamps, 

 were shown in action by a cuiTent from 60 Grove cells. 



The Electric Light is found to be most economical when a 

 single light of very great intensity is employed, but this is not 

 adapted for houses or narrow streets. It more nearly approaches 

 sun light in constitution than gas does, it heats the air less, and 

 perhaps vitiates it less, although small quantities of nitric acid and 

 prussic acid are foniied- As regards cost compared with gas, an exact 

 estimate is verj^ difficult on the present data, it will depend entirely 

 upon the special circumstances under which the light is used. The 

 allowance per hour for interest and depreciation — a very large item — 

 will depend upon the number of hours it is employed ; while the cost 

 of attendance may be either a serious item or nothing. In the news- 

 paper comparisons gas is often estimated at the Paris or American 

 prices, which are twice as much as those of London, and the 

 illuminating powers are often grossly misstated ; thus the Jablochkoff 

 light on the Embankment, really equal to about 150 standard 

 candles, is nearly always assumed to be equal to the light of 1000 

 candles. Only under the most favourable conditions does it appear 

 to be undeniabh' more economical than gas. But it will doubtless 

 be found veiy useful in concert halls and large reading rooms by 

 reason of its purity and coolness ; in ships, mines, and light-houses, 

 where it competes with oil ; and in factories where the attendance 

 and steam power will cost very little. For household purposes the 

 single light of great intensity would have to be i-eplaced by many 



