ON RADIANT HEAT. 
345 
both sides: also a plate of charcoal, and carmine spread upon wire-gauze 
(Table XI.): and again, using carmine blackened next the thermoscope, and 
plain; and black paper coated w'itb lamp-black next the thermoscope, and 
plain (Table XII.). 
The author thus arrives at the conclusion, “ under those circumstances in 
which the same bodies exhibit an unequal absorptive power, their radiating 
power is one and the same; and those differences which have hitherto been 
observed when they are not heated to the same extent, are therefore pure 
functions of the former, and independent of the latter." 
The conclusion, if we understand it rightly, would appear capable of being 
more easily stated, and indeed rendered at once obvious, from the distinctions 
at first pointed out : whence it is evident, that the rays of Species I. (as before 
described) from the cylinder, and those of Species II. from the lamp, will ne¬ 
cessarily act very unequally according to the texture and colour of the surface. 
But when a body has received the radiation, from whatever source, and 
converted it into heat of temperature, as in these cases, to an equalized de¬ 
gree, it will necessarily radiate it again in an equal degree with the same sur¬ 
face, from whatever species of rays it was originally obtained. 
Section IV. is headed, “Comparison of the Meat radiated from different 
bodies within a certain range of Temperature." 
The author commences by remarking that “all former observations upon 
radiation have only related to the quantities of heat emitted by different sub¬ 
stances at certain temperatures." The object of the present investigation is 
to ascertain whether there are any tpialitative differences; or, as the author 
expresses it, “whether the heat which radiates from certain bodies, at one 
and the same temperature or within certain limits of temperature, is of a 
different kind, according as it is emitted by different, bodies, or is excited in 
them iu a different way.” 
This inquiry was pursued by a series of experiments, in which (1) a ves¬ 
sel o( water at 212°, and (2) the flame of a lamp, had in contort with them 
various adhtf/iemanoits substances, such aa metal, porcelain, leather, wood, 
&c., in the heat given out by which the scries of screens gave exactly simi¬ 
lar scries of effects. As also with the heat from a hollow cylinder of 
topper or iron surrounding a flame, but when the direct radiation of the 
name was employed, the series of results were in proportions considerably 
different. (Tables XIII. to XVI.) 
fhe author indeed remarks at the conclusion, that these last differences 
? rc . ue to the heat transmitted by the screens, i. e. the heat conveyed by the 
uminous rays; as indeed would be manifest according to the views at first 
notice*!. b 
In another series, (1) an adiathermanous body at several temperatures from 
, , t0 212*, (2) the flame of a lamp, and (3) a metal cylinder round a flame 
pclow 234'\ were severally tried with the same series of screens; the results 
CaS( ’ 3 (1) and (3) being found exactly similar, in (2) in a ver^ different 
Proportion. 
J he same sources were next tried with two screens interposed; the first 
f n g successively, metal with holes, silk, ivory, &c., and each of these com- 
Mcd with the several screens of the former series. In all cases the results 
^proportional series. (Tables XVII. to XIX.) 
oothfir series was conducted with—1st, a flame, and 2nd, water at 212° ; 
ac 1 m succession with a screen used first plain ami then blackened, the 
being black glass, lac, ivory, paper, &e.; the results being always 
»s with the blackened surface, very similar in each case, and all less with 
toe hot water. (Tqblc XX.) 1 
