The Evolution of the Sciences 



this primitive matter having at a certain moment 

 proceeded too rapidly, a series of incompletely- 

 developed elements was produced, just as if 

 Nature had been prematurely delivered and space 

 peopled with abortions approximating to, but 

 distinct from, normal forms. According to this 

 holmium, erbium, gadolinium and dysprosium 

 would be only the meta-elements of yttrium, and 

 each of the known elements might, if we were 

 skilful enough to effect the chemical separations, 

 supply a whole series of satellites. 



Even if we neglect these rare elements, whose 

 identity is still somewhat doubtful, it is impos- 

 sible to avoid being struck by the profound 

 analogy of certain elements. Long ago Dumas, 

 interpreting these analogies, grouped in one 

 natural family fluorine, chlorine, bromine, iodine, 

 and in another sulphur, selenium and tellurium. 

 Similar natural associations unite the inert gases 

 of the air, which we have already enumerated, 

 the alkaline metals, the metals of the iron group. 

 The value of these analogies, and the existence 

 of a connection and a necessary interdepend- 

 ence between the elements of the same family 



is recognised by every chemist. 



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