a 
M. Melloni on the Radiations of Incandescent Bodies, 
This method, invented by Bouguer, to determine the relative 
intensities of different luminous sources, and employed by Draper 
to measure the quantities of light emitted by a strip of platina 
brought to different degrees of incandescence, is the only one by 
which we could hope for a successful result. The method of the 
equality of shadows, well known under the name of Rumford’s 
method, would have furnished in the researches of the learned 
American uncertain data, on account of the difficulty of estab- 
lishing an exact comparison between the accidental green tint 
introduced into the shadow enlightened by the yellow rays of t 
lati and the red light emitted by the ignited metal. 
As to the measures of the radiant heat, they were determined 
by the aid of the thermo-multiplier ; that admirable instrament 
which has revealed to science so many new properties of calorific 
radiations, and which still is rendering eminent revttowin in the 
hands of able cose far beyond the Alps. Professo: 
had only to arrange at a certain distance from his strip of platina 
a pana wa a vies a to observe for each phase of incandes- 
nee the deviation of the index of the galvanometer, to deter- 
mia the quantities sought. In this manner he obtained the 
numbers contained in the following table, divided into three col- 
umns. The first of these columns indicates the temperature for 
each degree of the scale of dilatation, commencing with me point 
of incandescence. The difference between each of the succes- 
sive terms of this series is thus constant, and equal to re The 
second and third columns give the corresponding quantities of 
light and heat. It is almost superfluous to add that the unity for 
light i is entirely independent of that for heat; and that the similar 
independent unities are not referrible to the same point of the scale. 
Temperature of the platinaw. Intensity of light. | Inteusity of heat. 
0 ie ‘87 
Paras 1:10 . 
pales 150 
ea: 1-80 
: 2:20 
ae 280 
bus 3:70 
ean 5 60 
0-34 680 
0-62 8-60 
173 10-00 
2:92 12:50 
4-40 15-50 a 
7:24 sgh | 
12-34 
Theinumbers obs the two latter iishisins shew evidential y that 
the augmentations of both these agents, though feeble at first, 
of light and heat, follow in the progression of | 
alogy that we havé just —— the p p 
Be 
very rapid at last; from which it results that the radia- 
