A Word of explanatiou as to the nature of valency-volumes : The existence of the law of valency-volumes involves the conclusion that each chemical atom in a crystal has its own special domain throughout which its influence is predominant as compared with that of any other atom. According to this conception the entire space occupied by the crystal can be regarded as portioned out among its constituent atoms, each atom having a cell allotted to it the boundaries of which consist of points at which the influence of some one or more neighbouring atoms is equal to that of the selected atom; thus no interstices are left between the cells.