DR GEORGE WILSON ON THE FINITE DIVISIBILITY OF MATTER. 83 
pressing force, such that the atmosphere would terminate in virtue of the law 
without any assumption of atoms. This may be proved by mathematical reason- 
ing. If we suppose the density of air to be as the square root of the compressing 
force, it will follow that, at the very limits of the atmosphere, the strata of equal 
thickness may observe in their densities such a law of proportion as is expressed 
by the numbers 7, 5,3, 1. For the compressing force on each being as the whole 
weight beyond it, will be for the four highest strata 16, 9, 4, and 1, of which the 
square roots are as 4, 3, 2, 1, or as 8, 6, 4,2; and, though these numbers are not 
exactly as the densities 7, 5, 3, 1, those who are a little acquainted with mathe- 
matical reasoning will see that the difference arises from taking so small a number 
of strata. If we were to make the strata indefinitely thin, as to avoid error we 
ought to do, the coincidence would be exact; and thus, according to this law, the 
series of strata terminates as we ascend, without any consideration of atoms.’’* 
My object in the succeeding argument is to shew, that, although the law 
which Wotiaston assumed to prevail in the higher regions of the atmosphere 
were in operation, it would not justify the conclusion which he supposed it to 
warrant. The discussion which follows differs from WHEWELL’s mode of disposing 
of the subject, in conceding to WoLLASTON his own law; and from that of Poisson 
and Dumas, in permitting him to take for granted as high a temperature as he 
pleases, provided only the atmosphere have reached a limit. 
On a little consideration of WoLLAstTon’s reasoning, it will appear, that all 
that he succeeded at the utmost in establishing was, that the atmosphere consists 
of a finite number of repelling molecules. He seems to have conceived that this 
was sufficient, and that no one would dispute his subsequent assumption, that 
these repelling molecules were ultimate particles or true atoms. 
But such an assumption is, on a twofold ground, inadmissible. The more im- 
portant chemical components of our atmosphere are, water-vapour, carbonic acid, 
oxygen, and nitrogen. Let us set aside for the time, as we are at liberty to do, 
the influence of the low temperature of the upper regions of the air in condensing 
the water, and perhaps also the carbonic acid ; and suppose our atmosphere, with 
a temperature at its boundary sufficient to retain all its constituents as elastic 
fluids, to find a limit, in virtue of the prevalence of Wot.aston’s law. Each gas 
would cease to expand for the same reason, and present a row of bounding mole- 
cules, which were prevented from falling towards the earth by the repulsion of 
the particles between it and them, and from receding from the earth by their own 
weight. But the molecules of water-vapour, and carbonic acid, brought in this 
way to a stand, would certainly not be ultimate particles or indivisible atoms. 
The molecule of water, on the simplest view of its constitution, namely, that the 
chemical equivalent corresponds to a single atom, would consist of at least two 
_* Philosophy of the Inductive Sciences, vol. i., p. 420, and Atheneum, 1839, pp. 724-7. 
