262 CLASSICS OF MODERN SCIENCE 

 continuous with those of the same layer already present; but those 

 molecules which form the adjacent surfaces of two layers do not 

 coalesce. This is a remarkable peculiarity in the formation of crys- 

 tals, and we are quite ignorant of its cause. We cannot yet perceive 

 why the new molecules, which are being deposited on the surface of a 

 crystal (already formed up to a certain point), do not coalesce and 

 become continuous with those already deposited, like the molecules in 

 each separate layer, instead of forming, as they do, a new layer ; and 

 why this new layer does not constantly increase in thickness, instead 

 of producing a second layer around the crystal, and so on. In the 

 meantime we can do no more than express the fact in the form of a 

 law, that the coalescing molecules are deposited rather along the sur- 

 face beside each other, than in the thickness upon one another, and 

 thus, as the breadth of the layer depends upon the size of the crystal, 

 so also the layer can attain only a certain thickness, and beyond this, 

 the molecules which are being deposited cannot coalesce with it, but 

 must form a new layer. 



If we now assume that bodies capable of imbibition could also 

 crystallize, the two modes of junction of the molecules should be 

 shown also by them. Their structure should also be laminated, at 

 least there is no perceptible reason for a difference in this particular, 

 as the very fact of layers being formed in common crystals shows that 

 the molecules need not be all joined together in the most exact manner 

 possible. The closest possible conjunction of the molecules takes place 

 only in the separate layers. In the common crystals this occurs by 

 apposition of the new molecules on the surface of those present and 

 coalescence with them. In bodies capable of imbibition, a much closer 

 union is possible, because in them the new molecules may be deposited 

 by intussusception between those already present. It is scarcely, 

 therefore, too bold an hypothesis to assume, that when bodies capable 

 of imbibition crystallize, their separate layers would increase by in- 

 tussusception ; and that this does not happen in ordinary crystals, 

 simply because it is impossible. 



Let us then imagine a portion of the crystal to be formed: new 

 molecules continue to be deposited, but do not coalesce with the por- 

 tion of the crystal already formed ; they unite with one another only, 

 and form a new layer, which, according to analogy with the common 

 crystals, may invest either the whole or a part of the crystal. We will 



