Professor Adams on the Theory of the Fhermometer. 125 
ton’s. I consider the above results and others contained 
in that same paper, as decisive against Mr. Dalton’ 5 hypo- 
thetical graduation of thermometers.” * 
The same writer{ defines a “ thermometer to ze an in- 
strument for measuring heat, founded on the principle, that 
the expansions of matter are proportional to the augmenta- 
tions of temperature. With regard to aeriform bodies, this 
principle is probably well founded; and hence our common 
thermometers may ‘be rendered just, by reducing their in- 
dications to those of an air thermometer. Solids, and still 
more liquids, expand unequally, by equal increments of 
heat, or intervals of temperature.” 
lice Dulong and Petit remark, ‘that Mr. Dalton, 
considering this question from a point of view much more 
elevated, has endeavoured to establish general laws appli- 
cable to the measurement of all temperatures. ‘These laws, 
it must be acknowledged, form an imposing whole by their 
regularity and simplicity. Unfortunately, “this skilful phi- 
losopher proceeded with too much rapidity to generalize 
his very ingenious notions, but' which depended on uncer- 
tain data. The consequence is, that there is scarcely one 
of his assertions but what is contradicted by the result of 
the researches, which we are now going to make known.” 
“Again, the well known uniformity in the principal phys- 
ical properties of all the gases, and particularly the perfect 
identity in the laws of their dilatation, render it very prob- 
able, that in this class of bodies, the disturbing causes to 
which I have adverted in my paper, have not the same in- 
fluence as in solids and liquids; and that consequently the 
changes in volume produced by the action of heat upon air 
and gases, are more immediately dependent upon the force 
which produces them. It is therefore very probable that 
the greatest number of the phenomena relating to heat will 
present themselves under a more simple form, if we meas- 
ure the temperatures by an air thermometer.{”’ 
“Tt seems probable” says Sir H. Davy, “that the capa- 
city (for heat) of solids and fluids is increased by expansion 
* Ure’s Dict. Art. Caloric. 
+ Art. Thermometer. 
t Quoted by Dr. Ure, Dict. Art. Caloric. 
