50 FRAGMENTS OF SCIENCE 



shown on the opposite page, which exhibits the distribu- 

 tion of heat in the spectrum of the electric light. In the 

 region of dark rays, beyond the red, the curve shoots up 

 to B, in a steep and massive peak — a kind of Matterhorn 

 of heat, which dwarfs the portion of the diagram c D E, 

 representing the luminous radiation. Indeed the idea 

 forced upon the mind by this diagram is that the light 

 rays are a mere insignificant appendage to the heat rays 

 represented by the area A B c D, thrown in, as it were, by 

 nature for the purpose of vision. 



The diagram drawn by Professor Miiller to represent 

 the distribution of heat in the solar spectrum is not by any 

 means so striking as that just described, and the reason, 

 doubtless, is that prior to reaching the earth the solar rays 

 have to traverse our atmosphere. By the aqueous vapor 

 there diffused, the summit of the peak representing the 

 sun's invisible radiation is cut off. A similar lowering of 

 the mountain of invisible heat is observed when the rays 

 from the electric light are permitted to pass through a film 

 of water, which acts upon them as the atmospheric vapor 

 acts upon the rays of the sun. 



7. Combustion hy Invisible Rays 



The sun's invisible rays far transcend the visible ones 

 in heating power, so that if the alleged performances of 

 Archimedes during the siege of Syracuse had any founda- 

 tion in fact, the dark solar rays would have been the phi- 

 losopher's chief agents of combustion. On a small scale 

 we can readily produce, with the purely invisible rays of 

 the electric light, all that Archimedes is said to have 

 performed with the sun's total radiation. Placing behind 

 the electric light a small concave mirror, the rays are 



