144 Count Rumford’s Enquiry concerning the Nature of Heat , 
bottom, had full liberty to escape upwards , and to make way for 
other particles of colder air to come into contact with the hot 
surface, and be heated, rarefied, and forced upwards, in their 
turns ; and, under these circumstances, it might reasonably be 
expected, that as much heat as possible would be communicated 
immediately to the air, by the hot body ; and that the heat so 
communicated would of course accelerate the cooling of that 
vessel. 
It was in fact cooled in a shorter time than the other. No. 5, 
which was suspended in a vertical position ; but the difference 
of the times of cooling was very small ; which indicates, if I am 
not mistaken, that a comparatively small quantity of the heat 
a hot body loses, when it is cooled in air, is communicated to 
that fluid ; much the greater part of it being sent off through 
the air, to a distance, in calorific rays. 
The vessel No. 5 was found to cool through the standard in- 
terval of 10 degrees in 384- minutes; and No. 6, which was in 
a reclined position, in 374- minutes. 
It will no doubt be remarked, that the vessel No. 5 cooled 
somewhat faster in this experiment than it had done in the two 
preceding experiments, (No. 29 and No. 30,) when it stood over 
a pewter platter, which (at the beginning of the experiment at 
least) was at the same temperature as the air of the room. 
The calorific rays from the bottom of the vessel, heating the 
platter in some small degree, and still more perhaps the upper 
surface of the perforated sheet of paper which covered it, the / 
frigorific rays from these bodies, were, on that account, some- 
what less powerful in lowering the temperature of the neigh- 
bouring hot body ; and the time of its cooling was consequently 
a little prolonged. 
