Dr. C. K. Akin on Calcescence. 35 



One interesting observation, made in the course of preparing 

 for the preceding experiments, may be worthy of mention. The 

 platinum being rendered incandescent in the focus of the mirror 

 by insolation, a film of water of some 2" thickness, contained 

 between thin sheets of glass, was interposed, and no other dia- 

 phragm, when the luminosity of the platinum quite disappeared, 

 just as upon the interposition of the red-glass diaphragm. By 

 the experiments of Masson and Jamin*, the absorption exerted 

 by glass and water of the thickness described upon the visible or 

 Newtonic rays is extremely small, and according to Professor 

 W. A. Miller f the same may be pronounced also with regard to 

 the absorption of the Ritteric rays ; but, on the other hand, it 

 is well known that glass, and even more so water, very power- 

 fully absorb the invisible Herschellic rays. It is evident, therefore, 

 that the sudden disappearance of the incandescence of the plati- 

 num-foil upon the interposition of the above water-and-glass 

 diaphragm is owing mainly to the abstraction of a great amount 

 of Herschellic rays from the incident beam. Hence it is proved 

 that in the first-described experiment, where all the three species 

 of rays impinge upon the platinum, the Herschellic rays contribute 

 to the production of incandescence — that is to say, of luminous or 

 Newtonic rays — though this does not actually prove that Her- 

 schellic rays by themselves are capable of causing incandescence J. 

 It might, besides, be objected to the above inference, that the 

 ceasing of incandescence, in the case described, might possibly be 

 owing to the loss of luminous and other rays by reflexion at the 

 several surfaces of the diaphragm which had been interposed. 

 This objection, however, may be obviated by simply remarking 

 that, upon employing a thinner film of water — the diaphragm 

 being otherwise similarly constructed, and therefore involving the 



* Comptes Rendus, vol. xxxi. p. 14 (1850). 



t Proceedings of the Royal Society, No. 51. 



X [A diaphragm of green glass acts in the same manner as the water 

 diaphragm ; that is to say, by interposing such glass between the mirror 

 and the platinum at its focus, the production of incandescence is prevented, 

 the incandescence making its appearance as soon as the diaphragm is 

 omitted. It might be (and indeed it has been) said that in this case, as in 

 that of the water, the Newtonic rays which are incident originate vibrations, 

 corresponding to Newtonic rays, on the part of the platinum-particles, and 

 that the function of the Herschellic rays which are added (upon the omis- 

 sion of the water diaphragm, for instance) is only to increase those vibra- 

 tions and to render them perceptible. It is difficult to conceive, however, 

 that an agent which is capable of increasing a certain mechanical effect 

 should not be capable also of originating it ; and I am therefore inclined to 

 consider the fact adduced in the text, and the corresponding one relating 

 to green glass, as really, though indirectly, proving the possibility of ray- 

 transmutations implying an elevation instead of a degradation of the rays in 

 the scale of refrangibilities.] 



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