128 Professor Adams on the Theory of the Thermometer. 
in the exchequer. This rod has, since this adjustment, 
been universally agreed upon as the standard of the meas- 
urement of lengths in England, and every other country 
where the English measures have been used, and all oth- 
er linear measures have been adjusted in reference to it. 
The French, after examining all the standards of linear 
measure furnished by nature, agreed upon the ,,4,°557 part 
of the length of the meridian, as their standard, and this, by 
the name of metre, forms the basis of their regularand beau- 
tiful metrical system. The dollar, containing 371.26 grains 
of pure silver, and 44.75 grains of copper, is agreed upon in 
the United States, as the standard to-which all other coins, 
as well as all monies of account, are to be referred. The 
general agreement to consider these as standards of measure 
of their own kind, is what constitutes them such standards. 
The case is the same with the thermometer. Until the 
late attempts to introduce hypothetical considerations into 
its construction, the dilatation of mercury was universally 
agreed upon as the standard for measuring the: different de- 
grees of energy of caloric, i. e. as the standard for measur- 
ing temperature. The whole dilatation between the deter- 
minate points, is divided into a convenient number of equal 
parts; (60,100 and 180 are the principal numbers which 
have been used,) and the scale which results from this 
graduation is conventionally used to measure all tempera- 
tures between its extreme points. Itis with as much rea- 
son, that the thermometric scale is equally divided into 180, 
or any other number of equal parts, as that the yard is divi- 
ded into 3, 36, &c. equal parts. Even if the hypothesis were, 
beyond question, true, that caloric is a material substance, 
and that the introduction of ten parts of a given quantity of 
itinto the mercury of the thermometer should expand it 
from 32° to 122°, while nine parts should be sufficient to 
expand it from 122° to 212°; still the circumstance ought 
not to affect the graduation; because the thermometer is 
designed to measure the energy of the action of caloric, and 
not the quantity of it introduced or disengaged. It is one 
thing to measure the quantity of caloric received into a 
body, or removed from it, and another to measure the in- 
tensity of its action. ‘These by no means necessarily cor- 
respond with each other. : 
