Prof. Norton on Molecular Physics. 889 



which the energy of the molecular forces depend. It is conceiv- 

 able that such differences may result from the heat evolved in 

 the process of crystallization. Let fig. 3, d, b, c, d, e, &c, be a 

 line of particles crystalli- „ 



zing in regular succession. e l ^' d ' 



When a unites with 5, the ^ ^ ^ ^, ^ ^ ^ 

 heat given out will expand <^~^W""w~ i W*""W"~w~" W"" 

 the atmosphere of c; and it 



is possible that, after this effect has been produced, the expanded 

 atmosphere wall not become condensed, under the operation of 

 the crystallizing forces, as much as it otherwise w r ould have 

 been, and hence that the molecular attractive force of c will 

 be less than would have otherwise resulted. If the attraction 

 between b and c should thus be materially lessened, there 

 would be in consequence less heat evolved in the union of 

 the two, and so the attractive force of d would be less weak- 

 ened than that of c has been. Accordingly, in the union of 

 c and d an excess of heat would again be given out. In this 

 way a series of alternations in the intensity of the cohesive 

 attraction might be brought about along the line of crystallized 

 molecules. 



It will be observed that the same fundamental idea pervades 

 all the explanations that have now been given of changes of 

 molecular aggregation, whether these are attended with a change 

 of state, or only with a change of density and form. This is 

 the idea that the physical and mechanical condition of a rnole- 

 cule may change with varying circumstances, and that it may 

 undergo a permanent change, although the temperature should 

 remain the same. The change of condition consists simply in 

 the expansion or contraction of the electric atmosphere of the 

 molecule (p. 382). We have recognized, also, that while the 

 processes of transformation are going on, the normal distribu- 

 tion of the electric fether, that forms the atmosphere of a mole- 

 cule, may become disturbed, and that thus a transient electric 

 polarity of the molecule may be induced which may play an im- 

 portant part in the process. 



Upon the theory of crystallization here offered, the pheno- 

 menon of dimorphism, and all changes of form, in the same crys- 

 tal, produced by heat and external causes generally, are but 

 simple results of the modifications superinduced by these causes, 

 in the form or distance from the central atoms of the molecular 

 atmospheres — that is, in the physical features of the molecules, 

 upon which the system of crystallization in every instance depends. 



[To be continued.] 



