CHAP, i.] CONSTITUTION OF MATTER. 5 



All these great laws, slowly evolved by observation and ex- 

 periment, have transformed into a solid scientific theory the 

 brilliant but vague intuition of the thinkers of ancient Greece. 

 With ground so firm to rest on, chemistry has been able to 

 particularise more, to study in some sort the individual cha- 

 racter of atoms ; in scientific language, it has arrived at the 

 notion of atomicity. 



Atoms have as general characteristics extension, impenetra- 

 bility, indestructibility, and eternal activity. But these general 

 characteristics exclude not a number of specific differences. 

 The progress of chemistry will no doubt show us what amount 

 of truth there is in the hypotheses of Dumas and of Lockyer, 

 according to which the simple bodies of chemistry as it now 

 exists are merely indecomposed bodies. According to this as- 

 sumption our metals and our metalloids are simple modifi- 

 cations of a single substance, probably hydrogen, the atoms 

 thereof forming different molecular groupings. In the present 

 state of science, these ideas, as yet purely hypothetical, can 

 be passed by ; and relying for the present on the great laws 

 of Dal ton, Ampere, Dulong, and Petit, we have the right to 

 consider the simple bodies of contemporary chemistry as repre- 

 senting groups of atoms identical among themselves in each 

 simple body, but specifically different from one simple body 

 to another. Now each of these atomic species has its individual 

 energy, its own affinities. In the group of the other atomic 

 species it has friends, it has indifferents, it has enemies. It 

 willingly unites itself to the first, neglects the second, refuses, 

 on the contrary, to combine with the last. Moreover, this faculty 

 of attracting and of being attracted attains in each atomic 

 species a different degree of energy. Whence we may conclude 

 that there are in the different atomic species differences of mass 

 and of form. In aggregating themselves thus, according to their 

 affinities, atoms arrange themselves into small systems, having in 

 each body a special structure. These atomic systems are called 

 molecules. 



The atoms of alkaline metals, such as potassium and sodium, 



