206 HABIT AND INTELLIGENCE. 



[chap. 



Molecular be defined as the science of the various states of molecular 

 defined! aggregation : it includes the theory of the gaseous or 

 vaporous, the liquid, and the solid states of substances, 

 and consequently of evaporation and freezing ; of cohesion 

 and capillarity, of solution, of gaseous and liquid diffu- 

 sion, of osmose, and of various other kindred subjects. 

 Crystallo- In strictuess of definition, crystallography is a branch of 

 molecular physics, but the facts of crystallography are so 

 distinct and so peculiar that it is much better to treat 

 it as a separate science. It is sufficiently obvious that 

 molecular physics comes before chemistry in the series, 

 because the simplest facts of chemistry would be unin- 

 telligible without some knowledge of molecular physics — 

 enough, at least, to understand what is meant by solution 

 or evaporation. Crystallography comes after chemistry, 

 because every crystalline species is a distinct substance 

 having its own peculiar chemical constitution, which is 

 equally characteristic of it with its " crystallographic 

 elements ; " and this, of course, can be learned only from 

 chemistry ; while it is possible to understand chemistry 

 as the science of combinations and decompositions without 

 reference to the facts of crystallization, which indeed are 

 referred to in chemical writings only occasionally. 

 Two We now come to the sciences of life. These fall into 



frthe^ two very well-marked groups. The subject of the first 

 sciences group consists in the properties of organisms considered 

 YiYst^' merely as such : these properties belong partly to morpho- 

 those'of logy, or the science of organic forms, of which science 

 pertieTof Systematic natural history is a part ; and partly to physio- 

 organisms, logy, or the science of vital functions. These two, no 

 Morpho- cloubt, are both parts of biology, and they run into each 

 physio- other ; but they do not, I think, run into each other more 

 °^^" than do chemistry and crystallography ; indeed, crystal- 



lography is a morphological science, and its relation to 

 chemistry may be compared with the relation of organic 

 morphology to physiology. Physiology and morphology 

 are so distinct that systematic natural history, which is 

 in fact comparative morphology, is not necessarily nor 

 generally cultivated by the same persons who cultivate 



