Dr. C. K. Akin on Calcescence. 33 



teric rays, will be still more easy to produce by means of Her- 

 schellic rays, to which, for some reason or other, a greater heat- 

 ing power is universally acknowledged to belong, as it will be 

 possible also to produce by any given luminous or Newtonic 

 radiation incandescence of such intensity that some of the New- 

 tonic rays emitted should exceed in refrangibility the incident. 

 In other words, through the production of incandescence by 

 irradiation, or more particularly insolation, the transmutations 

 previously denoted by (8) and (10) might be accomplished. 



6. Experiments.- — To test the exactness of the preceding infer- 

 ences, the author, conjointly with Mr. G. Griffith, Deputy-Pro- 

 fessor of Experimental Philosophy in the University of Oxford, 

 has instituted the following experiments. At the focus of 

 an ordinary concave glass mirror, measuring some 2' across*, 

 and irradiated by the sun, a piece of platinum-foil was exposed, 

 attached to the bottom of an opake tube, so that the back side 

 of the foil might be observed free from the interference of any 

 extraneous light, such light only being seen as the foil itself 

 might emit on becoming incandescent. On days of powerful 

 sunshine the platinum became vividly incandescent, and, viewed 

 by means of a pocket-spectroscope (which was inserted in the 

 above-mentioned tube), a spectrum exhibiting all the visible or 

 Newtonic rays might be observed. On placing, however, in the 

 path of the reflected cone of rays, between the mirror and its 

 focus, a sheet of monochromatic red glass (which, of all sub- 

 stances capable of absorbing the more refrangible part of the 

 spectrum, allows the less refrangible part perhaps the freest 

 access), the incandescence was found to be extinguished, or at 

 least to become so faint as to be of doubtful visibility. It was 

 needless to try, under these circumstances, whether the rays 

 reflected by the mirror were capable of producing incandescence 

 after having traversed a diaphragm allowing access only to Her- 

 schellic rays, and absorbing all the rest. 



Having found the mirror by itself thus far inefficient, it was 

 intended to resort to an expedient founded on the following con- 

 siderations. Let the heating effect of the rays transmitted by 

 the diaphragm of red glass, in the above experiment, be desig- 

 nated by a, and that of the rays absorbed by the same by /3. 

 It having been found, as mentioned before, that (ot+/3) was 

 sufficient for the production of incandescence, let the experiment 

 be made as first described — that is to say, the mirror be ex- 

 posed to the sun, the platinum placed in its focus, and the red 

 glass be interposed — but let the platinum besides be connected 

 with a galvanic battery capable of replacing to it the heating 

 effect /3, lost by absorption in the diaphragm ; then it appears 

 * [The principal focal distance was 2^\] 



Phil. Mag. S. 4. Vol. 29. No. 193. Jan. 1865. D 



