on some of the leading doctrines of caloric , &c. 343 
attending all the other methods; and scarcely capable of 
being exactly appreciated at high temperatures with the 
apparatus of Professor Robison. 
The space over which the vapour extends in my instrument, - 
need never be greater than half an inch of a barometer tube, 
against the side of which part the oblong bulb of a delicate 
thermometer rests, so as to indicate the true temperature. 
And though the liquid and incumbent vapour are thus always 
restricted to the summit of the barometer tube, we can, not- 
withstanding, measure its progressive range of elasticity, from 
zero of Fahrenheit to one hundred, or even two hundred, 
degrees above the boiling point of water, from an elasticity of 
0.07 of an inch, to that capable of sustaining 14 feet, or even 36 
of mercury. Fig. 1 (PL XIX.) represents the construction 
employed for temperatures under and a little above the boil- 
ing point. Fig. 2 and 3 are used for higher temperatures ; 
the last is the more convenient of the two. Each was sus- 
pended from a lofty window ceiling, and placed in a truly 
vertical position by means of a plumb line. 
One simple principle pervades the whole train of experi- 
ments ; which is, that the progressive increase of elastic force 
developed by heat from the liquid, incumbent on the mercury 
at 1 1 ' l ", is measured by the length of column which must be 
added over L, the primitive level below, in order to restore 
the quicksilver to its primitive level above, at /. These two 
stations, or points of departure, are nicely defined by a ring 
of fine platina wire twisted 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 
