124 Professor Adams on the Theory of the Thermometer. 
the expansion of the same liquid is not uniform for the in- 
crease of heat. Mr. Dalton having found that the dilata- 
tions of water are nearly as the squares of the temperatures 
reckoning from 32°, or the maximum of condensation, in- 
fers that the law is equally applicable to all other homoge- 
neous liquids; and he conceives the slight deviation from 
this law eo in water, arises from the unequal expan- 
sions in the mercury of the thermometer. If an instrument 
of this kind be so constructed as to accord with the unequai 
dilatations, the degrees will besmaller between pi od 122°, 
than between 122° and 212°. 
Dr. Ure says, “ if the body selected for inglielai by its 
increase of bulk, the increase of heat, suffered equal ex- 
pansions by equal increments of the calorific power, then 
the instrument would be perfect, and we should have a just 
thermometer or pyrometer. But-it is very doubtful wheth- 
er any substance, solid, liquid or aeriform, preserves this 
equable relation between. its increase of volume and in- 
crease of heat.” 
Again, “I thinkitindeed highly exababley that every species 
of matter, both solid and liquid, follows an inereasing rate in 
its enlargement by caloric. Each portion that enters into a 
body, must weaken the antagonist force, cohesion, and must 
therefore render more efficacious the operation of the next 
portion that is introduced. Let 1000 represent the cohe- 
sive attraction at the commencement, then, after receiving 
one increment of caloric, it will Became 1000—1=999. 
Since the next unit of that divellent agent will have to com- 
bat only this diminished cohesive force, it will produce an 
effect greater than the first, in the proportion of 1000 to 
999, and so on in continued progression. . That the increas - 
ing ratio is, however, greatly Jess than Mr.Dalton main- 
tains, may, I think, be clearly demonstrated.” 
Dr. Ure also says, that “ by means of two admirable mi- 
crometer microscopes of Mr. Troughton’s construction, at- 
tached to a peculiar pyrometer, I found, that between the 
temperatures of melting ice, and the 540° Fahr. the apparent 
elongations of rods of | Fie! copper and iron, corresponded 
pari passu with the indications of two mercurial thermome- 
ters of singular nicety, made by Mr. Crighton of Glasgow, 
one of which cost three guineas, and the other two, and 
they were compared with a very fine one of Mr. Trough¢ 
