Atoms. 193 



Let it be supposed that the alleged homogeneity 

 were as real as now it is imaginary. Let the 

 appeal be allowed which all logical atomists 

 make to the case of isomeric bodies, and espe- 

 cially to that of allotropic varieties. Let such 

 varieties of appearance as those presented by 

 carbon 1 and phosphorus 2 be attributed, not to 

 any qualitative cause, but to a different group- 

 ing of the atoms ; the morphological differences, 

 if adequately obtained, will still contribute no 

 explanation of the observed variations of at- 

 tribute. Vary in imagination, as you please, 

 the adjustments of their homologous sides, so 

 as to build molecules of several types, the 

 question will still remain unanswered, " What 

 is there in the arrangement a b c to occasion 

 ' activity ' in phosphorus, while the arrangement 

 b a c produces ' inertness ? ' " Where the pro- 

 ducts differ only in geometrical properties, and 

 consequently in optical, the explanation may 

 be admissible, the form and the laying of the 

 bricks determining the outline and the density 

 of the structure. But by no device can the 

 deduction be extended from the physical to the 



1 Charcoal, black-lead, and diamond. 



2 In the yellow, semi-transparent, inflammable form ; 

 and again as an opaque, dark red substance, combustible 

 only at a much higher temperature. 



O 



