on some of the leading doctrines of caloric, &c. 345 
mercurial column which we must add over L, in order to 
overcome it, and restore the quicksilver under l to its zero or 
initial level, when the platina ring becomes once more a tan- 
gent to the mercury.* 
At E a piece of cork is fixed, between the parallel legs of 
the syphon, to sustain it, and to serve as a point by which 
the whole is steadily suspended. 
For temperatures above the boiling point, the part of the 
syphon under E is evidently superfluous, merely containing 
in its two legs a useless weight of equipoised mercury. 
Accordingly for high heats, the apparatus fig. 2, or 3, is 
employed, and the same method of procedure is adopted. 
The aperture at O, fig. 3, admits the bulb of the thermo- 
meter, which rests as usual on l". The recurved part of the 
tube is filled with mercury, and then a little liquid is passed 
through it to the sealed end. Heat is now applied by an 
argand flame to the bottom of C, which is filled with oil or 
water, and the temperature is kept steadily at 212 0 for some 
minutes. Then a few drops of quicksilver may require to be 
added to D" till L" and V be in the same horizontal plane. 
The farther conduct of the experiment differs in no respect 
from what has been already described. The liquid in C is 
progressively heated, and at each stage mercury is progres- 
sively added over L" to restore the initial level, or volume 
at l", by equipoising the progressive elasticity. The column 
above L'' being measured, represents the succession of elastic 
forces. When this column is wished to extend very high, 
the vertical tube requires to be placed for support in the 
groove of a long wooden prism. 
* Rings of other metals will not suit ; for their expansions being much greater 
than that of glass, they become loose with the elevation of temperature. 
