Prof. Tyndall on Calorescence, 445 



permitted me to use a battery of 100 cells. In other experi- 

 ments I employed two batteries, one of 100 cells and one of 70, 

 making use of two lamps, two mirrors, and two niters, and con- 

 verging the heat of both lamps in opposite directions upon the 

 same point. When a leaf of platinum was placed at the com- 

 mon focus, the converged beams struck it at opposite sides, and 

 raised it to dazzling whiteness. I am persuaded that the metal 

 could be fused, if the platinum-black upon its surface could be 

 retained. But this was immediately dissipated by the intense 

 heat, and, the reflecting-power of the metal coming into play, 

 the absorption was so much lowered that fusion was not effected. 

 By coating the platinum with lampblack it has been brought to 

 the verge of fusion, the incipient yielding of the mass being per- 

 fectly apparent after it had cooled. Here, however, as in the 

 case of the platinized platinum, the absorbing substance disap- 

 pears too quickly. Copper and aluminium, however, when thus 

 treated, are speedily burnt up. 



§ 8. Thus far I have dealt exclusively with the invisible radia- 

 tion of the electric light ; but all solid bodies raised to incan- 

 descence emit these invisible calorific rays. The denser the in- 

 candescent body, moreover, the more powerful is its obscure 

 radiation. We possess at the Royal Institution very dense 

 cylinders of lime for the production of the Drummond light ; 

 and when a copious oxyhydrogen-flame is projected against one 

 of them it shines with an intense yellowish light, while the ob- 

 scure radiation is exceedingly powerful. Filtering the latter 

 from the total emission by the solution of iodine, all the effects 

 of combustion and calorescence described in the foregoing pages 

 may be obtained at the focus of the invisible rays. The light 

 obtained by projecting the oxyhydrogen-flame upon compressed 

 magnesia, after the manner of Signor Carlevaris, is whiter than 

 that emitted by our lime ; but the substance being light and 

 spongy, its obscure radiation is surpassed by that of our more 

 solid cylinders*. 



The invisible rays of the sun have also been transmuted. A 



* The discovery of fluorescence by Professor Stokes naturally excited 

 speculation as to the possibility of a change of refrangibility in the opposite 

 direction. Mr. Grove, I believe, made various experiments with a view to 

 effect such a change; but very soon after the publication of Professor 

 Stokes's memoir, Dr. Miller pointed to the lime-light itself as an instance 

 of raised refrangibility. From its inability to penetrate glass screens, he 

 inferred that the radiation of the oxyhydrogen-flame was almost wholly 

 extra-red, an inference the truth of which has been since established by 

 direct prismatic analysis. The intense light produced by the oxyhydrogen- 

 flame when projected upon lime must, he concluded, involve a change of 

 period from slow to quick, or, in other words, a virtual elevation of refran- 

 gibility. (Elements of Chemistry, 1855, p. 210.) 



