350 On the Theory of the [Nov. 
temperature than when near a small ove; because in the former 
case it must receive more calorific emanations than in the latter.” 
The second is repeated in the same work from Mr. Murray. “It 
is drawn from the difference in the radiation of two bodies, whose 
surfaces are different; such, for example, as a metallic surface and 
a blackened surface. ‘ Of different surfaces which at’a given tem- 
perature radiate different quantities of caloric, that which radiates 
least must be least powerful in returning caloric to the thermometer, 
and must therefore have least effect in counteracting the reduction 
of temperature.” And in applying this general remark, the author 
of the objection concludes from it, that if the theory of the equili- 
brium were true, it would follow that the blackened surface (which 
radiates most) ought to preduce a Jess degree of cold than the me- 
tallic surface (which radiates least). : 
I may attempt shortly to explain what is merely hinted at in the 
objection such as I have transcribed it. “Iwo bodies colder than the 
room are supposed, I conceive, to be presented to a thermometer, 
one of them terminated by a metallic surface, the other by a black- 
ened surface. It is known that the blackened body will soonest 
acquire the temperature of the place, and therefore will sink the 
thermometer most powerfully during the time of its heating. 
The author of the objection seems to think that, according to the 
theory of equilibrium, the contrary ought to happen, because the 
black body radiates more powerfully than the metallic surface; and 
‘decause this radiation, in part compensating the loss which the ther- 
mometer experiences from its own radiation, ought to be most effi- 
cacious in that of the two bodies, which radiates most abundantly. 
The third objection is likewise by Mr. Murray. It is drawn from 
the following experiment. A conical metallic tube, about 18 inches 
long, one inch in diameter at its narrowest extremity, and five 
inches at its widest, polished internally, so as to make a good re- 
flector, is placed in a horizontal situation. A very sensible thermo-' 
meter is placed at the widest end, and a matrass full of ice at the 
other. The thermometer sinks a very little. The experiment is 
now reversed ; so that the thermometer occupies’ the narrow end, 
while the matrass is placed at the widest extremity. In this case 
the thermometer sinks much more rapidly than in the preceding. 
This appears to the author of the objection incompatible with the 
theory of the equilibrium; doubtless because he conceives that the 
calorific rays ought to be condensed in the second situation of the 
tube, and thereby render the cooling of the thermometer Jess sen- 
sible. 
This experiment originated with Count Rumford (Memoir on 
Heat, 1804, p. 146); and he proposed it as a proof of the frigo- 
rific undulations, which he admitted, and which he compared to the 
sonorous waves. This objection may be proposed in a much more 
simple form. Ina place where the temperature is uniform, let a 
_ thermometer be presented to the narrow end of the tube: no rise 
