of Snow around Plants, 245 



at »33°.5. Here, then, we perceive a body heated under the 

 action of calorific radiation, producing an effect two or three 

 times greater than the direct rays of the source of the heat it- 

 self.* But, after what we have already said, it may readily be 

 understood how this should happen. 



Let us divide the radiating heat which directly strikes the 

 ther mo-electrical pile into 100 equal parts, and let us suppose 

 that ten of these parts are absorbed, and the rest are reflected. 

 Again, if the interposed sheet of paper, after being itself heated 

 from the source of heat, radiates to the pile only twenty-five 

 parts^of the hccit, and if, of these twenty-five, there are only five 

 which are reflected, and twenty which are absorbed ; then it is 

 clear that the heat communicated by the paper, although more 

 feeble by three-fourths than the heat direct from the source, will 

 nevertheless heat the active side of the pile twice as much, 

 and will consequently produce an action which is twofold more 

 intense. 



But it will l)e here demanded, if snow has really the proper- 

 ty, like the carbonate of lead, of absorbing different kinds of 

 radiated heat in different proportions ? The following experi- 

 ments will supply the answer to this inquiry.-f- 



One winter's day, when the temperature was at 2°.5 below 

 zero, the sky being cloudy, the air tranquil, and the ground 

 covered with recent snow, I placed the thermo-electrical pile, 



* Although we here employed flame, it is not to be concluded that the 

 experiment requires the presence of light ; for, in transmitting the calorific 

 rays through black and completely opaque glass, before using them, an opera-^ 

 tion which very thoroughly disengages them from all concomitant light, the 

 interposition of paper still gives a considerable augmentation in the devia- 

 tion of the galvanometer. In fact, this obscure radiation, which directly 

 produces from 10° to 11° of deviation, gave from 18° to 19° when it wasal- 

 sorbed by the sheet of dark grey paper, and then transmitted upon the 

 whitened pile. This experiment, which I repeat with the greatest facility 

 to any one wishing to witness it, alone suffices completely to overturn the 

 theories by means of which some wish to account for the present pheno- 

 mena and other analogous actions, alleging it is an actual transformation of 

 light into heat. 



+ These experiments upon snow are extracted from a somewhat extend- 

 ed work, which was long ago commenced, upon the absorbing and emissive 

 powers of bodies in general, and which is not yet finished. I publish them 

 in this detached way, because they appear to me to give a complete answer 

 to the question now agitated by M. Fusinieri. 



