LIGHT AND ITS ARTIFICIAL PRODUCTION. 299 



The aim, on the whole, is then to raise the incaudescent substances 

 to the highest possible temperature even at the expense of reducing 

 the size of the luminous area. In this sense the Argand burner with 

 chimney corresponds to a great improvement over the fish-tail burner, 

 just as does the petroleum lamj) of to-day over the oil lamp of the ancients. 

 In both cases an increase in temperature of the combining gases and 

 therefore of the incandescent carbon particles is produced. And while 

 the former is not important practically, the intensity increases as the 

 fifth power of the temperature, so that the flame of an Argand burner 

 is only about half as expensive as that of a fish-tail burner. Still 

 cheajier is the gaslight obtained from a Siemen's regenerative burner, 

 in which the gas before combustion is heated up by the heat otherwise 

 carried ofi:" by the products of combustion, and by this means the tem- 

 perature of the flame is still further increased. 



Cheapest of all is, however, the Welsbach light, because the temper- 

 ature of combustion is still higher than that of the regenerative burner. 

 The mantle had to be constructed such that a large part of it would 

 assume a high temperature (2,01)0° absolute) and had to be at the same 

 time of such a composition as to radiate almost as freely as carbon. 

 Both objects have been attained by Auer von Welsbach to whom, there- 

 fore, great credit is due. 



In the acetylene light the incandescence is also due to highly heated 

 carbon, as mentioned above, but, judging from the whiteness of the 

 light produced, its temperature must far exceed that of the Argand 

 burner. Although the price of acetylene light is dearer at present 

 than gaslight, it is principally due to the excessive cost of the calcium 

 carbide, from which the acetelyne is produced. If both acetylene gas 

 and ordinary illuminating gas could be furnished at the same price the 

 acetylene would be cheapest of all, the price being under these circum- 

 stances .005 cent per hour per candle power. 



But we could reason similarly in regard to the cost of electric light 

 and of petroleum light. The relative cost as given in the table de])ends 

 on the assumptions made in the second and fourth columns. 



The struggle for supremacy will never end, for much can still be 

 attained if the directions j)ointed out by science are followed. There 

 are, however, many difficulties to be overcome before we can expect to 

 ri'alize the ideal source of illumination theoretically possible. 



