DIVISIBILITY OF MATTER ATOMIC THEORY. 71 



others that may yet be discovered ? Or, in sight of this 

 difficulty, may we presume that many of the number 

 are really compounds of simpler elements, though 

 possibly beyond the reach of discovery as such? or 

 allo tropic conditions of the same element, as Dumas 

 conjectures regarding chlorine, iodine, and bromine ? 

 The whole question enters so deeply into the theory of 

 the material world, that we are bound to follow it as 

 far as reason and analogy will carry us, awaiting those 

 future disclosures which time is sure to afford. That 

 they will contract the catalogue of elements, up to this 

 time constantly increased in number, is my confident 

 belief. 



Seeking aid to this enquiry from other parts of 

 science, Crystallography is perhaps that most fertile of 

 suggestion. It deals with determinate figures, created 

 by the mutual actions of atomic parts, the simple atom 

 or the compounded molecule. This atomicity to use a 

 recent term in the structure of crystals is expressed 

 not only in their modes of aggregation, but also in 

 their optical axes and other relations to light ; and 

 further, in those internal changes of structure, already 

 noticed, which occur without change of outward form, 

 and those more special cases where the primitive form 

 of the crystal determines its mode of change when sub- 

 jected to heat. Other instances might be given, justi- 

 fying the notion of definite figure of atoms from the 

 analogy of crystalline accretions. If we have mathe- 

 matical forms of crystals, we may fairly presume such 

 to exist in the ultimate atoms composing them. If we 

 can reduce the primitive forms to three only, the same 



