DR GEORGE WILSON ON THE FINITE DIVISIBILITY OF MATTER. 83 



pressing force, such that the atmosphere would terminate in vu-tue of the law 

 without any assumption of atoms. This may be proved by mathematical reason- 

 ing. If we suppose the density of ah* 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 then- 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, wiU 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 WoLLASTON 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 temperatm-e as he 

 pleases, provided only the atmosphere have reached a limit. 



On a little consideration of Wollaston'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 idtimate 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 temperatm-e 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 suflacient to retain all its constituents as elastic 

 fluids, to find a limit, in virtue of the prevalence of Wollaston's law. Each gas 

 woidd 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 certauily 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 Athengenm, 1839, pp. 724-7. 



