and the Mode of its Communication . 131 
place, by the superior efficacy of the calorific rays which pro- 
ceeded from the blackened animal substance. 
On repeating this experiment a great number of times, and 
when the water in the vessels was at different degrees of tem- 
perature, (the temperature being the same in the two vessels, 
in each experiment,) the results uniformly indicated, that calorific 
rays were thrown off from the black surface, in greater abundance 
than from the equal surface which was not blackened. 
Although the results of these experiments appeared to me to 
be so perfectly conclusive as to establish the fact in question, 
beyond all possibility of doubt, yet, in so interesting an enquiry/ 
I was desirous, by varying my experiments, to bring, if possible, 
a variety of proofs, to support the important conclusions which 
result from it. 
Exper. No. 28. Having covered the two large cylindrical 
vessels. No. 3 and No. 4, with gold-beater’s skin, I painted one 
of them black, with Indian ink ; and, filling them both with 
boiling hot water, I exposed them to cool, in the manner already 
often described, in the air of a quiet room. 
No. 4, which was blackened , cooled through the standard in- 
terval of 10 degrees in 23I- minutes; while the other, No. 3, 
which was not blackened, took up 28 minutes, in cooling through 
the same interval. 
In a former experiment, (No. 25,) the instrument No. 4, 
covered with gold-beater’s skin, but not blackened, had taken 
up 27-! minutes, in cooling through the given interval, as we 
have before seen. 
The results of these experiments do not stand in need of illus- 
tration; and I shall leave to physicians and physiologists to deter- 
mine what advantages may be derived from a knowledge of the 
S 2 
