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X. — On WoUaston's Argument from the Limitatimi of the Atmosphere, as to the 

 Finite Divisibility of Matter. By Geoege Wilson, M.D., Lecturer on 

 Chemistry. 



[Read 21st April 1845.] 



In the year 1822, Dr Wollaston published a remarkable paper " on the finite 

 extent of the atmosphere."* Its object is to establish, by observations on the 

 motions of certain of the heavenly bodies, that our atmosphere does not extend 

 into free space, and to deduce from this limitation in its extent, the conclusion, 

 that the air necessarily consists of particles " no longer divisible by repulsion of 

 their parts ;" i. e. of true atoms. From this there is the further inference, that, 

 " since the law of definite proportions discovered by chemists, is the same for all 

 kinds of matter, whether solid or fluid, or elastic, if it can be ascertained that any 

 one body consists of particles no longer divisible, we then can scarcelydoubt that all 

 other bodies are similarly constituted." In other words, the existence of a limit to 

 the earth's atmosphere is declared to supply a demonstration of the finite divisibility 

 of matter. 



In pursuing this argument, Wollaston first discusses the question, What is 

 the probable height to which the earth's atmosphere extends? And after stating, 

 that, from the known laws of the elasticity of the atmosphere, we should infer that 

 it extends to the height of 40 miles, with properties yet unimpaired by extreme 

 rarefaction, he proceeds to say, " Beyond this limit we are left to conjectures 

 founded on the supposed divisibility of matter ; and if this be infinite, so also must 

 be the extent of our atmosphere. But if air consist of any ultimate pai-ticles no 

 longer divisible, then must expansion of the medium composed of them cease at 

 that distance where the force of gravity downwards, upon a single particle, is. 

 equal to the resistance arising from the repulsive force of the medium." Wollas- 

 ton, it will be observed, takes for granted two things, \stly. He assumes that the 

 law which is known to connect the density of the air with the compressing force, 

 near the surface of the earth, prevails, without change, to the limit of the atmo- 

 sphere. 2dly, He identifies the divisibility of the mass with that of its component 

 parts or molecules. If the molecule be infinitely divisible, the mass will be so 

 also, and vice versa j so that if the divisibility (finite or infinite) of either be as- 

 certained, that of the other will thereby be ascertained also. Now, the atmo- 

 sphere is not merely divisible, but, consisting like other gases of mutually repulsive 

 particles, contains within itself a power of division. We have only, therefore, tu 



* Philosophical Transactions, 1822, p. 89. 



