42 New experimental Researches 
the primitive level below, in order to restore the quicksilver to 
its primitive level above, at 4. These two stations, or points of 
departure, are nicely defined by a ring of fine platina wire twist- 
ed firmly around the tube.” 
At the commencement of the experiment, after the liquid well 
freed from air has been let up, the quicksilver is made a tangent 
to the edge of the upper ring, by cautiously pouring mercury in 
a slender stream into the open leg of the syphon D. The level 
ring below is then carefully adjusted. 
From the mode of conducting my experiments, there remained 
always a quantity of liquid in contact with the vapour, a circum- 
stance essential to accuracy in this research. 
Snppose the temperature of the water or the oil in A to be 
52° F., as denoted by a delicate thermometer, or by the lique- 
faction of ice ; communicate heat to the cylinder A, by means 
of two Argand flames, playing gently on its shoulder at each side. 
When the thermometer indicates 42°, modify the flames, or re- 
anoye them, so as to maintain an uniform temperature for a few 
minutes. A film or line of light will now be perceived between 
the mercury and the ring at /, as is seen under the vernier of a 
mountain barometer when it is raised a few feet off the ground. 
Were the tube at / and L of equal area, or were the relation of 
the areas experimentally determined, then the rise of the quick- 
silver above L would be one half, or a known submultiple of the 
total depression, equivalent to the additional elasticity of the 
vapour at 42° above that at 32°. Since the depressions, how- 
ever, for 30 or 40 degrees in this part of the scale are exceed- 
ingly small, one half of the quantity can scarcely be ascertained 
with suitable precision, even after taking the above precautions. 
And besides, the other sources of error, or at least embarrass- 
ment, from the inequalities of the tube, and from the lengthening 
space occupied by the vapour, as the temperature ascends, ren- 
der this method of reduction very ineligible. 
By the other plan we avoid all these evils. For whatever ad- 
ditional elasticity we communicate to the vapour above 4, it will 
be faithfully represented and measured, by the mercurial column 
which we inust add over L, in order ta overcome it, and restore 
the quicksilver under / to its zero or initial level, when the pla- 
tina ring becomes once more a tangent 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 poit, the part of the sy- 
* Rings of other metals will not snit; for, their expansions being much 
greater than that of glass, they become loose with the elevation of tem- 
perature. 
phon 
