THE CONSTITUTION OF MATTER. 4 
so as almost to equal the earth’s volume, and the atoms of 
that sphere enlarged in the same proportion, they will then 
have a diameter greater than that of a shot, and less than 
that of an orange. In other words, an atom is to a globe 
the size of a pea what an apple is to the terrestrial globe. 
By arguments of quite another kind, drawn in part from the 
study of chemical molecules, in part from the phenomena 
of capillarity, Gaudin has ascertained, for the dimension of 
the smallest particles of matter, figures very nearly the 
same as Thomson’s. The maximum distance apart of the 
chemical atoms in molecules is the ten-millionth part of 5, 
of aninch. Gaudin follows Thomson in the attempt to give 
some sensible notion of the truly amazing minuteness of a 
dimension like this. He calculates, upon this estimate, the 
number of chemical atoms contained in about the size of a 
pin’s-head, and he finds that the number requires for its ex- 
pression the figure eight followed by twenty-one ciphers. 
So that, if we attempted to count the number of metallic 
atoms contained in a large pin’s-head, separating each sec- 
ond ten millions of them, we should need to continue the 
operation for more than 250,000 years ! 
There are, then, atoms in matter, and atomism is a fact, 
whenever we rest in the affirmation of the existence of 
atoms. But these are not the real principles, the simple 
and irreducible elements of the world. After decompos- 
ing sensible matter into atoms, we must subject the latter 
to an analysis of the same kind. Let us, then, consider 
any two heterogeneous atoms whatever, an atom of iron 
and an atom of hydrogen, for instance, and examine in 
what respect they can really, essentially, differ from each 
other. What is it which at bottom truly distinguishes 
these two atoms, as atoms? It is not any peculiarity of 
form, solidity, fluidity, hardness, sonorousness, brightness, 
because these properties evidently depend on the mutual 
arrangement and disposition of atoms, that is, because 
