X.—On Wollaston’s Argument from the Limitation of the Atmosphere, as to the 
Finite Divisibility of Matter. By George Wuson, M.D., Lecturer on 
Chemistry. 
[Read 21st April 1845.] 
In the year 1822, Dr Woxttaston 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 ;” 7. ¢. 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 scarcely doubt 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, WotuasTon 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 particles 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.” Wo.ias- 
TON, it will be observed, takes for granted two things. sty, 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 ; 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, to 
* Philosophical Transactions, 1822, p. 89. 
