224 FRAGMENTS OF SCIENCE. 



those rays they acquire no heat ; still one of the substances, 

 sugar, is heated so highly by the concentrated beam of the 

 electric lamp that it first smokes violently and then inflames, 

 while the other substance, salt, is barely warmed at the 

 focus. Here, again, are two perfectly transparent liquids 

 placed in a test-tube at the focus ; one of them boils in a 

 couple of seconds, while the other in a similar position is 

 hardly warmed. The boiling-point of the first liquid is 78 

 C., which is speedily reached; that of the second liquid is 

 only 48 C., which is never reached at all. These anoma- 

 lies are entirely due to the unseen element which mingles 

 with the luminous rays of the electric beam, and, indeed, 

 constitutes 90 per cent, of its calorific power. 



I have here a substance by which these dark rays may 

 be detached from the total emission of the electric lamp. 

 This ray-filter is a black liquid that is to say, black as 

 pitch to the luminous, but bright as a diamond to the non- 

 luminous radiation. It mercilessly cuts off the former, but 

 allows the latter free transmission. I bring these invisible 

 rays to a focus at a distance of several feet frcm the electric 

 lamp ; the dark rays form there an invisible image of the 

 source from which they issue. By proper means this in- 

 visible image may be transformed into a visible one of 'daz- 

 zling brightness. I could, moreover, show you, if .time per- 

 mitted, how out of those perfectly dark rays we might ex- 

 tract, by a process of transmutation, all the colors of the 

 solar spectrum. I could also prove to you that those rays, 

 powerful as they are, and sufficient to fuse many metals, 

 may be permitted to enter the eye and to break upon the 

 retina without producing the least luminous impression. 



The dark rays are now collected before you ; you see 

 nothing at their place of convergence ; with a proper ther- 

 mometer it could be proved that even the air at the focus 

 is just as cold as the surrounding air. And mark the con- 

 clusion to which this leads'. It proves the ether at the focus 



