THE BANISHMENT OF NIGHT 



when heated to certain temperatures. Some sub- 

 stances were known to be peculiarly adapted to this 

 purpose, such as lumps of lime, and for many years the 

 calcium light or "lime-light" as it is popularly called, 

 had been in use for special purposes, and was the most 

 intense light known. This light is made by heating 

 a block of lime to the highest practicable temperature 

 by means of a blast of oxygen and coal gas; but such 

 lights were too complicated and expensive for general 

 purposes. It had been determined even as early as the 

 beginning of the nineteenth century, however, that the 

 high temperature necessary for producing this light 

 was due in part at least to the fact that such a large 

 amount of material had to be raised to incandescence. 

 It was evident, therefore, that if a small amount of some 

 such substance as lime and magnesia could be spread 

 out so as to present a large surface in a small space, such 

 as is represented by basket-work, sufficient heat for 

 making it incandescent might be obtained from an 

 ordinary gas-and-air blowpipe. 



Here then was the germ of the "mantle" idea; and 

 such an apparatus, known as the Clamond mantle, 

 which was made of threads of calcined magnesia, was 

 shown at the Crystal Palace Exhibition, in London, 

 in 1882. Curiously enough, this mantle and burner 

 worked in an inverted position, the mantle being sus- 

 pended bottom upwards below the burner through 

 which the blast of gas was forced. The light given by 

 this mantle was most brilliant little short of the older 

 calcium light, in fact but the device itself was too 

 complicated to be of service for ordinary lighting 



VOL. VI. 14 [ 2O9 ] 



