64 DIVISIBILITY OF MATTER ATOMIC THEORY. 



had the largest share in this act of progress ; though 

 the general conception is one which might well be 

 derived from observation of the diversities of matter, 

 and of those endless changes and interchanges which 

 can only be effected by particles of infinite smallness. 

 The microscope, too, though far short of its present 

 perfection, had already disclosed organisms so minute, 

 yet so perfect in their several forms, as to suggest at 

 once an elaboration from atoms the apspy re aAa^o-ra 

 of matter. But the doctrine of Definite Proportion in 

 chemical compounds, well established, made that of 

 atoms a direct necessity ; and the principles embodied 

 in this doctrine have derived from the genius and 

 labours of chemists a certain mathematical character 

 even in the formulae used for their expression. A 

 period of little more than sixty years, dating from the 

 first rude outline of Dalton, comprises all these signal 

 discoveries best expounded by terms which denote 

 their dependence on the properties and relations of 

 atoms, such as isomerism, isomorphism, allotropy, 

 substitution, types, homologous series, atomic weights, 

 &c. These terms may hereafter merge in others more 

 general ; but meanwhile they are needed to express 

 phenomena forming that great body of connected 

 science which under the name of Chemistry (a name 

 of feeble origin for what it now denotes) deals with 

 the infinitesimal parts of matter in all its forms with 

 their mutual actions and affinities, and their connexions 

 with those great natural forces, light, heat, electricity, 

 &c., which call these relations into activity. Forces 

 act upon matter by changing in one way or other the 



