1865.] Physics. 321 



now to be referred to, the rays from the electric light were converged 

 by a small concave glass mirror silvered at the back. It was brought 

 so near the electric light as to cast an image of the coal points five or 

 six inches in advance of the light. A solution of iodine in bisulphide 

 of carbon contained in a rock-salt cell was then placed in front of the 

 lamp ; the whole of the luminous rays were thereby cut off, the dark 

 heat rays only coming to a focus: 



In this focus of intense heat, in which nothing whatever is 

 visible to the sight, what will take place if a solid body is introduced ? 

 Will the body become red or white hot ; that is to say, will the long 

 vibrations of the heat rays be exalted in refrangibility and vibrate in a 

 quicker period ? We know that rays can be lowered in refrangibility, 

 but the possibility of rays of low refrangibility being raised higher has 

 been denied by some physicists on theoretical grounds. The experi- 

 ments of Professor Tyndall have conclusively settled the question, and 

 proved that rays can be transmitted upwards, as well as downwards. 



With an eight-inch mirror behind the electric light, the opaque 

 solution of iodine in front, and the focus of invisible rays about six 

 inches distant from the electric light, the following effects have been 

 obtained : — Wood painted black, when brought into the dark focus, emits 

 copious volumes of smoke, and is soon kindled at the two spots on 

 which the images of the two coal points fall. A piece of brown paper 

 placed near the focus soon shows a burning surface which spreads over 

 a considerable space, the paper finally bursting into flame. The end 

 of a cigar placed at the dark focus is instantly ignited. A piece of 

 charcoal suspended in a receiver of oxygen is ignited in the dark focus 

 and caused to burn brilliantly. A mixture of oxygen and hydrogen is 

 exploded in the dark focus by the ignition of its envelope. Magne- 

 sium wire presented suitably to the focus, burns with its intensely 

 luminous flame. In all these cases the effect was due in part to che- 

 mical action; this, however, may be excluded. For instance, plati- 

 nized platinum in thin leaf may be rendered white hot, and on it is 

 depicted an incandescent image of the coal points. When the points 

 are drawn apart or caused to ajiproack each other, their incandescent 

 images conform to their motion. Professor Tyndall proposes that the 

 assemblage of phenomena here described, and others to be referred to 

 in his completed memoirs, should be expressed by the term " calores- 

 cence." This word involves no hypothesis, and it harmonizes well 

 with the term fluorescence, now universally employed with reference to 

 the more refrangible end of the spectrum. 



The subject of dissociation of the elements of compound gases at 

 high temperature is being energetically worked out by H. Ste. Claire 

 Deville.* He has previously shown that both water and carbonic acid 

 possess the apparently paradoxical property of partially resolving 

 themselves into their elements when heated to a much lower point 

 than that attained by the combination of the elements of which they 

 are composed. The great difficulty in experiments of this kind is to 

 prevent the decomposition from being immediately followed by a re- 



* ' Chemical News,' vol. x. p. 285, and vol. xi. p. 2-90. 



