LAWS OF DECREMENT. 



291 



Fig. 324. 



Let us now suppose a decrement by 2 rows in 

 breadth to have taken place on the edge of a similar 

 parallelepiped. If we imagine the first plate of 

 molecules which is superimposed on the primary 

 plane to be deficient in two rows of single molecules ; 

 and if we imagine two additional rows of molecules 

 abstracted from the second plate, and so on, the plane 

 i k would be produced, and the lines i g, g &, would 

 be the edges of the defect of the primary form occa- 

 sioned by this decrement. 



But it is evident that the line g k is to the line g /, 

 as 4 m is to 2 ft, or as 2 m to ??, this being the ratio 

 which the number of molecules abstracted in the 

 direction g f, bears to the number deficient in the 

 direction of g d. 



From these examples we find that whenever a 

 decrement takes place on the edges of any parallele- 

 piped, replacing that edge by a plane, the edges of 

 the defect will be to those edges of the primary form, 

 of which they are respectively parts, in the ratio of 

 the numbers of molecules abstracted from each su- 

 perimposed plate in the direction of the same edges 

 respectively; and that such ratio will express the 

 law of decrement by which the new plane has been 

 produced. 



2o2 



