246 M. Melloni on the Cause of the speedi/ Melting 



blackened as usual, on one of the casements of my window. On 

 its one side I put an argand-lamp, and on the other a bent plate 

 of copper, heated posteriorly to about 400° by a spirit-lamp. 

 By this arrangement, each of the faces of the pile fronted a 

 source of radiating heat, in such a way that the two calorific 

 actions tended to compensate each other. I approximated the 

 feebler source till the corresponding galvanometer maintained 

 itself at the zero of the division. 



I then took a small copper tube, having the same dimensions 

 as the envelope of the pile, and provided like it with a stalk, by 

 which it might be introduced into the same support. This tube, 

 which was open at both ends, was divided perpendicularly into 

 two equal chambers, and into each of these I introduced pure 

 sn6w to a height corresponding to about half the length of the 

 thermo-electrical bundle (Jaisceau). 



I now removed from the stand or support the pile which we 

 have just described as placed between the argand-lamp and the 

 heated plate of copper, and in its place I substituted the tube 

 filled with snow. Each of the two portions of included snow 

 was thus exposed to the action of a source of heat ; and the two 

 calorific radiations, at the places where they infringed upon the 

 corresponding snowy columns, were of equal intensity. But not- 

 withstanding this, the snow column which was contained in the 

 cavity turned towards the plate of copper heated to 400°, melt- 

 ed much more readily than did the other in the opposite cavity. 

 This trial concluded, I again filled the apparatus with snow, 

 and replaced it upon the stand of the pile, taking care, at the 

 same time, now to turn towards the lamp the side which pre- 

 viously fronted the heated plate. Still, however, the melting 

 was accomplished much more rapidly on the side of this latter 

 source of heat ; and so it was every time, and as often as I 

 continued the experiment. The mean time for the total disap- 

 pearance of the snow on the side of the lamp was about nine 

 minutes and a half, whilst on the side of the heated plate, the 

 mean time did not exceed four minutes. 



This experiment proves, in the most satisfactory manner, 



that the calorific rays from different sources are absorbed in 



different quantities by snow as well as by carbonate of lead. I 



i^all now add two other observations of the same kind, which 



