14 BEPORT — 1882. 



Tyndall used in his experiments may be taken at 10 Ohms, the current 



qg.g 

 produced in the arc would be - " lo i i ~ "^ ^™peres (allowing one 



Ohm for the leads), and the power consumed 10x4^ = 160 Watts; the 

 light power of such an arc would be about 150 candles, and, compai'ing 

 this with an arc of 3,308 candles produced by 1,162 Watts, wc find that 



r V i.e., 7-3 times the electric energy produce (-TTTr )> i.e., 22 



times the amount of light measured horizontally. If, therefore, in Dr. 



Tyndall's arc -jyth of the radiant energy emitted was visible as light, it 



1 22'0 

 follows that in a powerful arc of 3,300 candles, — - x -— -, or fully ^-, are 



luminous rays. In the case of the incandescent light (say a Swan light 

 of 20 candle power) we find in practice that 9 times as much power has 

 to be expended as in the case of the arc light ; hence ^ x J- = ^V P^''*' of 

 the power is given out as luminous rays, as against ^'jth in Dr. Tyndall's 

 incandescent platinum — a result suificiently approximate considering the 

 wide difference of conditions under which the two are compared. 



These results are not only of obvious practical value, but they seem to 

 establish a fixed relation between current, temperature, and light produced, 

 which may serve as a means to determine temperatures exceeding the 

 melting point of platinum with greater accuracy than has hitherto been 

 possible by actinimetric methods in which the thickness of the luminous 

 atmosphere must necessarily exercise a disturbing influence. It is probably 

 owing to this circumstance that the temperature of the electric arc as well 

 as that of the solar photosphere has frequently been greatly over-estimated. 



The principal argument in favour of the electric light is furnished by 

 its immunity from products of combustion which not only heat the 

 lighted apartments, but substitute carbonic acid and deleterious sulphur 

 compounds for the oxygen upon which respiration depends ; the electric 

 light is white instead of yellow, and thus enables us to see pictures, furni- 

 ture, and flowers as by daylight ; it supports growing plants instead of 

 poisoning them, and by its means we can carry on photography and 

 many other industries at night as well as during the day. The objec- 

 tion frequently urged against the electric light, that it depends upon 

 the continuous motion of steam or gas engines, which are liable to 

 accidental stoppage, is met by the introduction into practical use of the 

 secondary battery ; this, although not embodying a new conception, has 

 lately been gi-eatly improved in power and constancy by Plante, Faure, 

 Volckmar, Sellon, and others, and promises to accomplish for electricity 

 what the gas-holder has done for the supply of gas and the accumulator 

 for hydraulic transmission of power. 



It can no longer be a matter of reasonable doubt, therefore, that 

 electric lighting will take its place as a public illuminant, and that, even 

 though its cost should be found greater than that of gas, it will be 

 preferred for the lighting of drawing-rooms and dining-rooms, theatres 



