86 FKAGMENTS OF SCIENCE. 



the total emission of the electric lamp. This ray-filter 

 is a liquid, black as pitch to the luminous, but bright 

 as a diamond to the non-luminous, radiation. It mer- 

 cilessly cuts off the former, but allows the latter free 

 transmission. When these invisible rays are brought 

 to a focus, at a distance of several feet from the electric 

 lamp, the dark rays form an invisible image of their 

 source. By proper means, this image may be trans- 

 formed into a visible one of dazzling brightness. It 

 might, moreover, be shown, if time permitted, how, out 

 of those perfectly dark rays, could be extracted, by a 

 process of transmutation, all the colours of the solar 

 spectrum. It might also be proved that those rays, 

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

 can be permitted to enter the eye, and to break upon 

 the retina, without producing the least luminous im- 

 pression. 



The dark rays being thus collected, you see nothing 

 at their place of convergence. With a proper thermo- 

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

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

 conclusion to which this leads. It proves the aether at 

 the focus to be practically detached from the air, that 

 the most violent aethereal motion may there exist, 

 without the least aerial motion. But, though you see 

 it not, there is sufficient heat at that focus to set 

 London on fire. The heat there is competent to raise 

 iron to a temperature at which it throws off brilliant 

 scintillations. It can heat platinum to whiteness, and 

 almost fuse that refractory metal. It actually can fuse 

 gold, silver, copper, and aluminium. The moment, 

 moreover, that wood is placed at the focus it bursts into 

 a blaze. 



It has been already affirmed that, whether as re- 

 gards radiation or absorption, the elementary atoms 



