164 Theory of Cryjlall'ifalhn . 



arrived at the figure of the fquare A' G'L' K' {fig. 32)*, 

 will, when they pafs that term, decreafe on all fides at the 

 lame time, fo that the following lamina will have for its fu- 

 perior face the fquare B 7 M'I'S' {fig. 33), lefs by one range 

 in every dire&ion than the fquare A' G' L' K' (j?§\ 32): 

 This fquare muft be difpofed above the preceding in fuch 

 a manner that the points c',/', g', b' ', {fig. 33), may eorre- 

 fpond with the points c,f, g, h {fig. 32). 



Figures 34, 35, 36 and 37 reprefent the four laminser 

 which ought to rife fucceffively above the preceding, under 

 this condition, that the fame letters muft corrcfpond as 

 above. The laft lamina will be reduced to a fingle cube, 

 diftinguifhed by *' {fig. 38), and which ought to reft upon 

 that pointed out by the fame letter fig. 37. 



It follows from what has been faid, that the laminae of fu- 

 perpofition applied on the bafe A B C D {fig. 29 and 30) 

 produce by the total of their decreafing edges four faces, 

 which, in proceeding from the points A, B, C, D, incline 

 one to another in the form of a pyramidal fummit. 



It is here to be remarked, that the edges in queftion have 

 lengths which begin by increafing, as may be fcen on in- 

 fpecting /m*. 31 and 32, and which then proceed decreafing, 

 as may be fecn by the following figures. It thence refults 

 that the facts produced by the fame edges increafe at firft, 

 and afterwards decreafe in breadth, fo that they become 

 quadrilaterals. Figure 39 reprefents one of thefe quadrila- 

 terals, in which the inferior angle C is confounded with the 

 angle C{fig. 29) of the nucleus; and the diagonal L Q, 

 reprefents the edgeL'G'of the lamina A' G' 1/ K' {fig.^2) y 

 which is the moft extended in the dire&ion of that edge. 

 And as the number of the laminae of fuperpofition which pro- 

 duce the triangle LCQ {fig. 3.9) is lefs than that of the lamina; 

 which produce the triangle LZQ, fince there is here only one 



* In the prefent cafe this figure takes place from the fecond lamina of 

 fuperpofition. By affurning a nucleus compofed of a greater number of 

 n:o!ecul'e, it is evident that we mould have a more remote boundary. 



rL lamina 



