<)2 



Count de Bournon on the Laumo7iite, 



Rctrogradations along the edges of the terminal faces formed by the incidence of these faces 

 on the sides of the prism, at an angle of 66° 38'. 







Angles formed by the 

 meeting of the new- 

 planes with the ter- 

 minal faces. 



i 









Number 

 of the 

 modifi- 

 cations. 



|{- 



Angles formed by the 

 meeting of the new 

 planes with those of the 

 prism. 



Angles formed by the 

 meeting of the new 

 planes with those of the 

 11th modification. 



Nature of tlie rc- 

 trogradations. 





11th. 



1! 

 p 



. . . 139% 10' ... . 



.... 107% 







Rctrogradation by 

 two rows. 





















12th. 



. . . 145% 9' . . . 



.... 101% 29' . . . . : 



.... 174% 1' . . . . 



Retrogradation by 

 three rows. 









Intermediate rctrogradations upon the acute angles of the terminal faces that concur in the 

 formation of the acute solid angles of the primitive crystal. 





Number 

 of the 

 modifi- 

 cations. 



l'h\ 



Angles which the 

 edge uniting the 

 newplanesforms 

 with the termi- 

 nal faces. 



Angleswhichthe 

 edge uniting the 

 newplanesforms 

 with the edgesof 

 92% 30'. 



Angles of inci- 

 deiice between 

 the new planes. 



Angles of inci- 

 dence between 

 the new phmes, 

 and the terminal 

 faces. 



Nature of the rc- 

 trogradations. 





13th. 



CO 



■J 



ii 



||- 



%% 



> 

 1 



. . 9S», 26' . . 



. . 13S%34' . . 



. . 136%58'-. . 



■ . . 110% 20' . 



Retrogradation bv 

 a single rov/, which 

 while it takes one 

 molecule from one 

 of the sides of the 

 acute angles, takes 

 two from the otiKT. 









14th. 



. . 81', 59' . . 



. . 153% 1' . . 



. . 134% S4' . . 



. . 82% 32' . . 



Retrogradation by 

 a single row in 

 breadth, and two 

 lamins in height 

 which, while it 

 takes one molecule 

 from one of the 

 sides of the acute 

 angles, takes two 

 from the other. 





