Dr. C. K. Akin on Calcescence. 43 



instances where the transmuting agent is a vapour*. The increase 

 of radiation exhibited in these experiments, at first sight, appears 

 equivalent to a creation of energy ; but, upon consideration, it is 

 easy to see that such need by no means be the case. Some direct 

 experiments might perhaps be made on this point. 



(2) The experiments before described, in which the platinum 

 was to be heated by electricity previously to the incidence of solar 

 rays, together with a remark mentioned below, led me to pro- 

 pose to myself an investigation of the absorptive powers of solids 

 for rays as dependent on temperature f- 



(3) In my original paper, since published in the Reports of the 

 British Association for 1863, I suggested an explanation of the 

 phenomena of ray-renovation, according to which the rays emitted 

 in the act of renovation are to be considered as resulting from a 

 species of interference between the incident or absorbed rays and 

 the rays spontaneously emitted by the renovating substance. In 

 order to test this view practically, I intended to try the following 

 experiment. Let a fluorescent substance be placed in front of a 

 thermo- multiplier, and between the multiplier and that substance 

 let an absorbing medium be placed, capable of eliminating New- 

 tonic rays of that very description which the substance in question 

 gives out in the act of fluorescence. The caloric equilibrium being 

 established whilst the substance does not fluoresce, it is evident 

 that, as soon as the substance begins to fluoresce, the caloric equi- 

 librium will be disturbed — supposing that in the act of fluores- 

 cence some of the rays originally emitted by the fluorescent matter 

 get, as it were, consumed (as they must in a case of interference), 

 and supposing also that no merely reflected rays are allowed to 

 pass from the fluorescent substance through the absorbing 

 medium on to the pile. 



(4) Finally, besides some other points not ripe enough to be 

 here mentioned, I purposed to investigate the Herschellic spectra 

 of the principal incandescent gases, that have recently been exa- 

 mined with regard to their Newtonic spectra. I also intended 

 to endeavour to procure thermographic impressions of Herschellic 

 spectra of all kinds.] 



London, December 1864. 



Corrigenda. 

 Vol. xxviii. p. 475, line 7, for § 207, i. read art. 2071. 



— p. 477> line 23, for centripetal read centrifugal. 



* Pogg. Ann. vol. cxxi. p. 510 (1864). 



t In Phil. Trans, vol. xxx. p. 977 (1719), it is stated, regarding a certain 

 metallic mirror, that "the glass [i. e. the mirror] growing hot burned with 

 much less force." This, I thought, might be a proof of the dependence of 

 absorption on temperature, although it is possible to assume that the fact 

 adverted to may have arisen from some other circumstances. 



