254 Master Minds of Modern Science 



eight per cent, of the power used to heat the filament. 

 The firefly and the glow-worm can give us points and a 

 beating, for they — and they alone — have the secret of pro- 

 ducing cold light. It is calculated that the luminous 

 efficiency of the firefly is between ninety-five and ninety- 

 seven per cent. Their light is true luminescence, whereas 

 our electric light is produced by heat. The creation of 

 cold light is one of the great tasks which is awaiting the 

 scientists of the present century. 



We have written at length about electric lighting 

 because we are most familiar with the electric current in 

 this form, yet it is only one of very many forms, of course, 

 in which electric power is employed. A great many indus- 

 tries depend so entirely on electric power that they could 

 not exist without such a supply. Calcium carbide, from 

 which acetylene gas is obtained, is made by mixing coke 

 and lime and shovelling them into the electric furnace of 

 which it is essentially a product. Carborundum, next to 

 the diamond the hardest substance in the world, is made 

 by the cheap electric power generated at Niagara Falls. 

 A few years ago aluminium, now used for all sorts of 

 things, from cooking-pots to flying-machines, was a mere 

 curiosity of the laboratory. This metal too we owe to 

 the electric furnace. The ore of aluminium is cheap 

 enough, for it is only a clay, but the amount of current 

 needed to make one ton of aluminium is no less than thirty 

 thousand units, or forty times as much as is required for 

 making a ton of steel. At Foyers, on Loch Ness, the British 

 Aluminium Company use a waterfall which gives thirty 

 thousand horse-power. 



Through increasing demand the supply of natural salt- 

 petre no longer meets the world's requirements. Saltpetre 

 provides nitric acid, which is essential in the manufacture 

 of explosives, while nitrogen is the most valuable of all 

 plant-fertilizers. To combat the famine in saltpetre, 

 nitrogen is now drawn from the air by a process which 



