OBSERVATIONS ON THE NATURE OF HEAT. 243 
I am treading upon novel and very uncertain ground ; but it is not 
more against reason, unaided by experiment, to suppose that any 
body will give off caloric, whether latent or in any other form, on the 
application of a suitable cause, than to suppose steam, which conveys 
to our senses or the thermometer a temperature no higher than 
boiling water, should, on its condensation, give off nearly 1000 
degrees more than is contained in boiling water. I say, the one sup- 
position is not more plausible than the other by reasoning simply. 
Though the one is known from its effects, the other may possibly 
be explained when our knowledge of the subject becomes more ac- 
curate and our instruments more delicate. 
On the whole, the increase of temperature on the metal being 
condensed, and the temperature always being in proportion to the 
condensation, seem to resemble much the overflowing of a vessel 
filled to the brim with water, on plunging any body into it; and if 
the latter fact be a proof of the impenetrability of water, the experi- 
ments of Berthollet, if they do not prove the same with regard to 
caloric, afford, at least, presumptive evidence in its favour. 
I come now to consider which of the hypotheses gives the most 
satisfactory explanation of the phenomena dependent upon caloric. 
It is a law nearly universal for all matter to expand by the addition 
of caloric: solids and fluids both observe this law. On this expan- 
sion something must enter between the particles, else there must be 
a vacuum ; and on the supposition that there is a vacwwm, how does 
it happen that the atmosphere does not follow its usual law, and 
rush towards the unoccupied space? If it did enter between the par- 
ticles of the expanded body, it is natural to suppose that the weight 
of that body would be increased; but the following experiment of 
Dr. Fordyce shews that increase of weight does not necessarily fol- 
low an increase of temperature. He put 1700 grains of water into a 
glass globe three inches in diameter, and sealed it hermetically, and 
then ascertained the weight of the whole. He next plunged the globe 
into a freezing mixture; where he kept it till part of the water was 
frozen, which he again weighed; and on comparing the weight of 
each trial, he found that the frozen water had gained about 1-60th 
part of a grain. These trials were repeated several times, more of 
the water being frozen each time, when a corresponding increase of 
weight was obtained. This would seem to prove that the weight of a 
body became less on the addition of caloric; and were ponderosity 
reckoned one of the properties of matter, it would militate against 
the materiality of caloric ; but as this property is merely relative anc 
