APPLICATIONS OF ELECTRIC LIGHT. 353 



considering the enormous progress of electro-magnetic appli- 

 cations made within the last few years, there is every ground 

 for hopefulness as to its ultimate success. 



In a lecture at the Royal Institution, in 1849,* Mr. Grove dis- 

 cussed certain practical applications of voltaic ignition and the 

 voltaic arc, such as eudiometry, lighting mines, street-lighting, 

 and light-houses. He had made some experiments six years 

 ago on the subject, and then on one occasion delivered a lecture 

 at the London Institution, the theatre being illuminated by 

 the voltaic arc. In preparing the lecture he had made a rough 

 calculation as to expense, and the matter appeared to him 

 (though attended with many practical difficulties) to be hopeful 

 and promising. By interposing a voltameter in the circuit 

 while the arc was produced the consumption in the battery 

 could be calculated ; for every chemical equivalent of hydrogen 

 evolved in the voltameter an equivalent of zinc, of sulphuric 

 acid, and one-third of an equivalent of nitric acid, would be 

 consumed in each cell of the battery. Supplying these data 

 for calculation, and making proper allowance for the amount 

 of water contained in the commercial acids, &c., the theore- 

 tical expense of a battery such as he was exhibiting (fifty cells 

 of the nitric acid combination, each platinum plate two inches 

 by four) would be about two shillings an hour. He had tested 

 by the photometric method of equality of shadows the inten- 

 sity of the light as compared with a common wax-candle, and 

 found that after the battery had been an hour at work the 

 voltaic light was to the candle as 1,444 to l - He did not take 

 this comparison of intensities as an absolutely fair practical 

 comparison, nor did he give the above as a practical calcula- 

 tion, but thought it would be safe if twice that expense, or four 

 shillings per hour, were assumed ; the actual expense of charg- 

 ing the battery for a given time of action bore this out. He 

 showed the inferiority of central as compared with separate 

 lights for street illumination, but for lighthouses, particularly 

 for an intermittent light at regular intervals, or for signal 

 lights, the application appeared to him to be reasonably ap- 

 proximate, and for more general purposes far from hopeless ; 



* Lit. Gaz., Feb. 24, 1849, 

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