592 THE POPULAR SCIENCE MONTHLY 



The close analogies which we have shown to exist between the 

 periodic and the zoological classifications would seem to point toward 

 a fundamental identity of principle in these two systems. I have en- 

 deavored to show that there are in the inorganic world the exact homo- 

 logues of some of the most important facts upon which the law of 

 organic evolution rests, L e., the evidence of the geological record and 

 of the embryological resemblances; to emphasize the importance of the 

 spectroscopic evidence ; and to show that the Periodic classification is in 

 its main aspects identical in its nature with the zoological classification. 

 These facts tend to indicate that the groups of the elements correspond 

 to the phyla of the organisms, in being the outward expression of a 

 process of evolution. The periodicity in the arrangement of the ele- 

 ments is expressive of the fact that in each family there is the same 

 plan of atomic structure, and a gradual and progressive change in this 

 structure as we traverse the groups from the inert gases to the halogens. 

 That it is an imperfect relationship is shown by its numerous contra- 

 dictions, already mentioned. These facts, however, harmonize en- 

 tirely with the evolutionary view, for zoological classifications show 

 just such irregularities. Moreover, according to the evolutionary view, 

 an element need not necessarily be smaller in atomic weight than the 

 next in the same series. The evolutionary view is entirely compatible 

 with those phenomena, which seem to be out of harmony with the 

 Periodic classification. 



If the species of organisms were few enough and their structure 

 simple enough, it seems likely that it would be possible to select some 

 common characteristic which would serve as a basis of periodicity cor- 

 responding to that in the elements. Conversely, as has already been 

 indicated, if the number of the elements were at all comparable to that 

 of organic species, it is probable that the Periodic relation would be 

 largely obscured by the great number of its exceptions. 



Without the knowledge of the fact of organic evolution, the arrange- 

 ment of animals and plants into classes, with their numerous group 

 resemblances and counter resemblances, must have seemed a purely 

 arbitrary one, having no basis in nature. 24 Similarly, when we con- 

 sider the characters of the elements of the same families, their close 

 resemblances to each other, and their minor resemblances to members of 

 other families, the irregularities of the Periodic classification, etc., it is 

 evident that we can coordinate these seemingly contradictory phenomena 

 into a coherent whole on the basis of the evolution of the elements. The 

 extraordinary relations disclosed by the Periodic classification are the 

 outward and manifest signs of the process to which atoms, like organ- 

 isms, owe their individual natures. The process begun in the one (the 

 atom) continues in the other (the organism). 



24 ' ' The propinquity of descent — the only known cause of the similarity of 

 organic beings — is the bond, hidden as it is by various degrees of modification, 

 which is partly revealed to us by our classification." Darwin, quoted by 

 Spencer, "Principles of Biology," Vol. I., p. 364. 



