on some of the leading doctrines of caloric, &c. 377 
highest station, the column of quicksilver equal on the stem 
to 3 x 180°, is sustained by the expansion of 60 parts ; at the 
middle point, 2 x 180° is supported by that of 61 ; and at 
212 0 there are 6 2 parts of mercury to sustain 180° in the tube. 
Or, to put it in another form, these three successive spaces 
on the scale are equal ; the first portion of mercury is pro- 
truded into it by the expansion of 62 parts in the bulb ; the 
second portion by the expansion of 61 ; and the third by that 
of 60. 
Therefore, if these three thermometric intervals of 180°, each 
of which holds an equal measure of mercury, contain also 
equal increments of temperature, as denoted by the equal 
increments of a metallic rod ; then, these three equal effects 
are produced from the unequal quantities of mercury (>2, 61, 
60. This liquid, then, must have an increasing rate of expan- 
sion, the inverse of these numbers, for every 180° of the scale, 
or ^2 , fr, That is to say, 60 parts at 572 0 do the same 
work by the same power of caloric, as 6T at 392 0 , and 6 2 at 
212°. 
I believe this to be the real nature of mercurial expansion, 
and the true condition of the thermometer; which is an 
equable measurer of heat, because the mercury possesses the 
above increasing rate of expansion. Were the mercury, on 
the contrary, absolutely uniform in its augmentations of 
volume by equal increments of heat, then for an instrument 
whose bulb alone in practice can be immersed, the three 
above ranges should have the corresponding parts of the 
scale shortened in the successive proportions of 62 to 63 ; 
61 to 63 ; and 60 to 63 ; quantities taken together nearly 
equal to 9 0 , or = 3 x ^ x 180 = . 
