LAWS OF DECREMENT. 



289 



We may conceive it possible to reduce this entire 

 rhomboid to the state of the modified one, by remov- 

 ing, in one mass, the triangular pyramid of molecules 

 d c f g, fig. 322, in which the supposed modified 

 crystal is deficient. 



The mass of molecules, therefore, in which any 

 secondary form is deficient) when compared with its 

 primary form, is equal to the number of molecules 

 abstracted in the production of that secondary form, 

 arranged in the same order as they would have been, if 

 they had completed the enlarged primary form. 



This mass, so arranged, being all the addition to 

 the secondary form which would be required to com- 

 plete the primary, will be called the defect of the 

 primary form, and it will be shewn presently that 

 the edges of this defect may be used in every instance, 

 to determine the decrement by which the secondary 

 plane is produced. 



Fig. 323. 





For the purpose of illustrating this proposition 

 further, let us observe the change which would have 

 taken place, if a parallelepiped of any kind, either right 

 or oblique, as a b c d e, fig. 323, had been modified 

 on one of its edges, by a decrement consisting of a 

 single row of molecules. 



whether that plane exposes the edges, solid angles, or planes of the 

 molecules. 



