FREE AND PERFECTLY ELASTIC MOLECULES IN A STATE OF MOTION. 47 
density of an atmosphere. The formula that corresponds to this line has the constant 
G = 22-6065 and cot H = 20-0023. 
It will be remarked that the line for Dalton’s ether (which, from its low 
boiling point, must have been nearly pure), Thompson’s pyroxilic spirit, and the well 
determined line for steam, are nearly parallel; is this parallelism perfect ? It is also 
remarkable that the projection of two experiments by Dalton on aqueous ammonia is 
exactly parallel with the steam line, and further, that the same parallelism is 
maintained by the vapours of liquefied ammoniacal gas and carbonic acid (by 
Thilorier). It would be extremely desirable if Dr. Faraday’s experiments on 
chlorine and the other more condensible gases could be repeated on a large scale so as 
to determine their position on the chart, and by two or three observations on each to 
eliminate the constants G and H. It is by such experiments and those of 
M. Cagniard de la Tour, made at the other extremity of the scale of heat and 
pressure, and likewise by Mr. Perkins, all of which may be classed under the head of 
chemical physics, that we may expect to extort from nature some of her most hidden 
secrets, to come in sight of new continents in the world of natural science, not dreamt 
of in our philosophy, because removed beyond the bounds of suggestive analogy. 
Such pressures appear to us great, and are certainly dangerous to operate with, but in 
respect to those which exist in nature, and that everywhere surround us, restrained by 
internal forces, they can only be considered as infinitesimal. 
Note C.—Temperature of Compressed Air. 
These changes of temperature are certainly much greater than are said to have 
been observed by Darwin, Dalton, and others. Not having access to the original 
account of these experiments, I am unable to ascertain how far they accord with the 
theory; but the specific heat of air is so small in comparison to that of the materials 
of which thermometers are composed that the actual difference of temperature in 
a single condensation or dilatation must be much greater than what is indicated by 
any thermometric apparatus. 
A more effectual way of ascertaining this seems to be by continually and quickly 
repeating the same condensation with different portions of air, so that after some time, 
by proper care, the condensing syringe ought to exhibit the temperature of the air at 
its maximum tension. 
If air is a medium we have in XVI. the means of computing the temperature that 
ought to be shown by a thermometer placed at the bottom of the syringe. 
Thus, t 0 , e Q being the temperature and tension of the air outside, e 1 the tension 
corresponding to the load on the eduction valve of the syringe ; then - = 
_ C 0 
and (t 0 461 ) ~ — 461 = t L , the temperature of the air when condensed. 
( t 0 + 461 Y 
U + 461/ ’ 
