THE ELECTRIC LIGHT 441 



ery, repeating Yolta's experiments, and extending them in 

 many ways. The light and heat of the voltaic circuit at- 

 tracted marked attention, and in the innumerable tests and 

 trials to which this question was subjected, the utility of 

 platinum and charcoal as means of exalting the light was 

 on all hands recognized. Mr. Children, with a battery 

 surpassing in strength all its predecessors, fused platinum 

 wires eighteen inches long, while "points of charcoal pro- 

 duced a light so vivid that the sunshine, compared with 

 it, appeared feeble." * Such effects reached their culmi- 

 nation when, in 1808, through the liberality of a few mem- 

 bers of the Eoyal Institution, Davy was enabled to con- 

 struct a battery of two thousand pairs of plates, with 

 which he afterward obtained calorific and luminous effects 

 far transcending anything previously observed. The arc 

 of flame between the carbon terminals was four inches 

 long, and by its heat quartz, sapphire, magnesia, and 

 lime, were melted like wax in a candle flame; while 

 fragments of diamond and plumbago rapidly disappeared 

 as if reduced to vapor.' 



The first condition to be fulfilled in the development 

 of heat and light by the electric current is that it shall 

 encounter and overcome resistance. Flowing through a 

 perfect conductor, no matter what the strength of the cur- 

 rent might be, neither heat nor light could be developed. 



» Davy, "Chemical Philosophy," p. 110. 



2 In the concluding lecture at the Royal Institution jn June, 1810, Davy 

 showed the action of this battery. He then fused iridium, the alloy of iridium 

 and osmium, and other refractory substances. "Philosophical Magazine," vol. 

 XXXV. p. 463. Quetelet assigns the first production of the spark between coal- 

 points to Ourtet in 1802. Davy certainly in that year showed the carbon light 

 with a battery of 150 pairs of plates in the theatre of the Royal Institution 

 ("Jour. Roy. Inst." vol. i. p. 166). 



