THE CONSTITUTION OF MATTER. 7 



so as almost to equal the earth's volume, and the atoms of 

 th^ft 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 -^ 

 of an inch. 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 



