Professor Adams on the Theory of the Thermometer. 129 
Again, wherever in the prceding quotations, a new grad- 
uation of the thermometer is suggested, the proposed grad- 
uation is not founded upon facts, but upon hypothesis. In 
the present state of our information, it is an hypothesis, and 
has not been proved to be a fact, that caloric is a material 
substance. When Dr. Ure says, “that solids and still 
more liquids expand unequally by equal increments of 
heat ;’’ the idea of its being a material substance and of 
its producing a mechanical effect is introduced. The same 
hypothesis is involved in the reasonings of all the writers 
which have been cited except the last: but in some, it is 
much more dexterously kept out of sight, by cautious lan- 
guage, than in others. Dr. Ure thinks in one passage, 
that with regard to aeriform bodies, the expansions give 
just indications of temperature; while in another, he 
is very doubtful, whether any substance solid, liquid or 
aeriform, can by the graduation, afford a true measure of 
temperature. His words have not been used, but his 
meaning has been given. When Dr. Ure says, that he 
considers an air thermometer as a just measure of tem- 
perature, he should have recollected, ‘ that between the 
limits of freezing (melting ice) and boiling water, a mer- 
curial and air thermometer did not: present any sensible 
discordance.”* This is the result of M. Gay Lussac, 
whose accuracy as an experimenter, has perhaps never 
been exceeded. The same relation, which M. Gay 
Lussac has shewn to exist between the mercurial and 
air thermometer, the experiments of Messrs. Lavoi- 
sier and Laplace, have proved to belong equally to the 
mercurial thermometer and most of the solid metals. 
‘© Les expériences de M. M. Lavoisseur et Laplace, sur la 
dilatation des corps solides, nous ont appris qu’ entre les 
tennes de la glace fondante et de |’eau bouillante, la dila- 
tation des metaux solides est sensiblement proportionnelle 
a celle du mercure. La meme proportionnalité subsiste 
encore dans ces limites entre les dilatations du mercure 
et celles des gasees. Ce resultat important a €té parfaite- 
ment établi par les expériences que M. Gay Lussac a 
faites dans ce dessein sur la dilatation des yaz.f— These 
* Dict. art. Caloric. 
+ Biot, Traité de physique, &c. I, 182. 
Von. VIII.—No. I, 17 
