346 
REPORT —1854. 
Another set, with a heated mass and with the hand at its natural tempera* 
ture for sources, gave similar results with various screens. (Table XXI.) 
This, the author says, “disproves the opinion of Forbes, that the heat 
emitted by boiling water and the hand must be considered as different." I 
am unable to find in what respect Prof. Forbes supposes them different. 
At the conclusion of this section the author adverts to two practical in* | 
ferences from what has preceded. 
(i. ) The fact, that the amount of heat absorbed by a given body is the same, 
from whatever source it was derived, is important in regard to the deter¬ 
mination of specific heats by the calorimeter ; for if the heat absorbed by the 
ice were different as it might be derived from different soured, no correct 
measure of specific heat would be obtained. That it is not so, ensures the 
accuracy of the results so tar as this source of error is concerned. 
(ii.) The second application is, that “ these results lead to a nevnuethod of 
ascertaining whether any substance transmits rays of beat or not' (235); 
that is, of determining whether any given instance of transmission of heat is 
determining whether any given 
really due to diathermancy, or is merely secondary radiation. 
Thus, to determine whether ivory e.g. is really diathermanous: the source 
of heat is a known adiathermanous substance kept heated by a lampJy'* 1 
effect is observed : a known diathermanous screen is then interposed and the 
effect again observed* the ivory is then substituted f*oi‘the adiaiherm3noui 
body and the direct effect equalized to the former; the same screen is then 
interposed, but now a greater effect is transmitted. It follows, that partot 
the original heat is transmitted directly by the ivory, along with that radial# 
from it; or the ivori/ is diathermanous . . 
Section V., on “ the Comparison of the amount of Heat diffusely reflcctea 
by different bodies,” refers to that kind of irregular reflexion, or disp<y ll>n 
(as it has been sometimes called) of the rays from the roughened, oral 
unpolished surfaces of bodies, and which is distinguished from regmar n> 
flexion, which is governed by the law of equal angles of reflexion and mo* 
deuce, by occurring equally at all angles. And the object is stated by t e 
author to be the determination “ whether beat, on diffuse reflexion, 
rirnces changes in its properties which distinguish it from that which is” 
reflected " (384*). 
1 lie heat being incident on a rough surface is of course partly 
and radiated again : to guard against, error from confounding this witn 
proper reflected heat, various and careful precautions were adopted. 
i he author then proceeds to detail the observations, which areofyolu ’ 
nous extent, and the results recorded in a long series of tables. ( la 
XXII. to XXXII. inclusive.) 
In all this first scries the source employed was an Argand lamp without i-- 
chimney, and in all eases the mode of operating was similar. , 
1 he unpolished surface under examination was exposed to the rays ol M 
amp, at different, distances and at different inclinations, and the direct 
noted: the experiment was then repeated with the insertion of a series of 
variously diathermanous screens. 
arrepfnn U ’ )8taDCft9 U9€!f * 08 reflectors were extremely varied; such as b^“ 
3ES& and difei "e«" «»»* " tom06CBM 
ori-'in oMltl'n. 1 . 1186 ran » e substances of animal, vegetable and [n j ,] '' 
the nercirn, '"^P 8 "'' 1 - *>»' »U colours and textures, were 
% these results, the author observes, “it is placed beyond all doubt, that 
