ATOMIC THEORY. 423 



relative magnitudes, though the results are still neither cer- 

 tain nor complete, yet the numerical relations and analogies 

 they already afford are very remarkable, and will probably 

 conduct to new and higher proofs of the doctrine before us. 

 In ascertaining the nearly identical atomic volume of certain 

 groups of elementary bodies, closely allied in chemical pro- 

 perties and found generally in close association in nature, 

 MM. Kopp and Schroder, to whom chiefly we owe these 

 researches, are evidently on a path which promises access to 

 yet untrodden fields of science. 



We shall advert but to two or three of the many general 

 relations which subsist between the Atomic theory and the 

 various branches of physical science. The first of them is 

 .expressed in the phenomena of Crystallisation those mutual 

 actions of the molecules of matter, whether simple or com- 

 pound, denoted by the assumption of regular or geometric 

 forms. Crystallisation may almost be defined as a conversion 

 of atomic numbers into a material configuration. In all the 

 vast variety and beauty of crystals, giving splendour to our 

 mineral cabinets, and illustrated by the labours of Hauy, 

 Mohr and Weiss, Wollaston, Brewster, Beudant, &c., we find 

 proof of the primitive tendency of atoms to group themselves 

 in certain definite figures; to build up, as it were, the 

 crystalline fabric in mathematical lines and proportions. 

 When to this we add the fact, that changes may take place 

 in the solid interior of a crystal without affecting its outer 

 form, we gain some idea of those wonderful workings of 

 molecules or atoms, which in their totality make up all the 

 phenomena of the material world. 



Connected with this topic, and perhaps but a more general 

 expression of the same physical law, comes in that great 

 principle of Polarity ; hard to define in its most extensive 

 sense, and yet so largely seen and proved in every part of 

 nature, that no science can be successfully pursued without 



