REPORT —1854. 
344 
conditions observed, that the effect of secondary radiation was fully guarded 
against. 
Hence the author draws the conclusion, “ that the passage of radiant heat 
through diathernianous bodies is not in immediate connexion with the tem¬ 
perature of the source, as w as probable from previous experiments; but is 
alone dependent upon the structure of the diathennanons substance, which 
is penetrated by certain rays of heat in a greater degree than by others, 
whether this occurs at a lower or a higher temperature.’’ 
In all this there appears nothing to remark, except perhaps the observa¬ 
tion that previous experiments might make a contrary result probable, which 
do. s not appear to be the case, since (ns already observed) the temperature 
of luminosity has been long known to be very different for different sub¬ 
stances. It were to be wished, that when the au thor speaks of “certain rays" 
being transmitted, he had more distinctly indicated the species to which they 
belong, but which seem to conform to the classification before noticed. 
Some further experiments were made on sources of different form and size; 
cubes and cylinders of hot water of several magnitudes, small and large 
(lames, having successively different screens interposed between them and the 
thermoscope. The results were very uniform for all the sources, proving 
that the differences in question produced none in the transmission, as indeed 
might have been expected. (Table V.) 
Section II. is “ On the Heating of Bodies by Radiant Heat" 
Here, after observing in general, as a well-known fact, that the effect is 
greatly influenced by the structure of the surface, he observes,— 
“ More recent experiments by B. Powell and Mellon! have shown that 
one and the same body is not uniformly heated by rays of heat emanating 
from different sources, which exert the same direct action upou a thermo- 
scope coated with lamp-black"(p.205). 
And he details some experiments (Table VI.), showing that with a lamp a 
gi eater effect is produced on a surface coated with black paper than one with 
carmine, but with dark beat, a less:—a result which might indeed have been 
expected from what was well underetood before tire date of the researches 
alludtd to, and which it was by no means their object to establish. 
A set of experiments (Table VII.) proved that for small thicknesses ol 
coating (within the limit of those employed by Leslie and IVJelloni), the 
absorption of heat is proportional to the thickness. 
ai>°, that “tfle temperature of a body, when the thickness increases, is 
» ^t! cm 11 ' H diathernianous to the rays transmitted to it.” 
JZrZT, '' “° n thc Pr °P cr, y of Radiating Heat in Bodies," the 
Z/Z TV Van T cases i " "hich the state of the surface, as in f 
to S,l T th scotched more or less closely, was observed ss 
wair. 1 (Table VJIJ) rad,at,on ’ wLe " the plates were kept heated by boiling 
cIu‘sion ,; ;; n ?;;f; im ; ntS . whh c ,°PP er (Table IX.) confirmed Melloni’s eon- 
elusion, that the action is purely mechanical. 
crewXhJcL S eL° f f Vp<,r ;- mente(TabIeX -)> the ^crease of radiation with *«• 
loni, that radiation ^ Coaf,,, £ confirms the conclusion of Rurnford and Me * 
The neSlt f° mmcncos * certain depth below the surface, 
the radiating tiower' erm,< ’ nt ? \ vas directed to answer the inquiry, 
to a given degree by rAv^fwH! ‘he same body vary according as it is heat 
distinctly in the mJLtivl ,I° Ql sources of heat?" The answer 
der, and the bodv f* s , ollrces G< Beat being a lamp and a hot cjbn- 
with carmineandwUh Ltn ? being fuccessively paper 
Uh lamp-black on the absorbing side, and lastly on 
