186 New experimental Researches 
oil of vitriol heated to 212°; ~.* part of the whole included 
mercury will now ascend above that part of the stem plunged in 
the liquid. The part actually exposed to the heat, and by whose 
expansion the colunin on the scale is supported, is only $2 of the 
initial mass. Augment the heat of the’oil till the instrument in- 
dicate 392°; we know that there remains now, under the imme- 
diate influence of the heat, &+ nearly of the original weight of 
mercury; and finally, at 572° , only “about £0 rest in the im- 
mersed a of the stem and bulb. 
3; or z!; parts may be considered as no longer subjected to 
the power of caloric. If the themometer stem were recurved near 
the bulb, the mercury in the stem placed horizontally would be 
cold; and this proposition would be almost exactly true. 
Now, since the calibre and divisions are uniform, the capacity 
of the tube from the point marked 212° to that marked 392°, 
and again from this to that opposite to 572°, is in each equal to 
its capacity from 32° to 212°, Hence these three equal capa- 
cities are filled by the expansions of the three unequal quantities 
of mercury 62, 61,60. At the highest station, the column of 
quicksilver equal on the stem to 3 x i80°, is sustained by the 
expansion of 60 parts; at the middle point, 2 x 180° is sup- 
ported by that of 61; and at 212° there are 62 parts of mer- 
cury 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 protruded into ic 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 62, 61,60. This liquid, 
then, must have an increasing rate of expansion, the inverse of 
these numbers, for every 180° of the seale, or 445, gs go. That 
is to to say, 60 parts at 572° do the same work by the same 
power of caloric, as 61 at 392°, and 62 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 in- 
creasing rate of expansion. Were the mercury, on the contrary, 
absolutely uniform in its augmentations of volume by equal in- 
crements of heat, then for an instrument whose bulb alone in 
practice can be immersed, the three above ranges should have 
* A minute fraction less; but we neéd not ‘complicate the statement 
with it. 
the 
