224 HISTORY OF MINERALOGY. 



forms, by means of the decrements of the successive 

 layers of integrant molecules. 



The latter of these discoveries had already been, 

 in some measure, anticipated by Bergman, who had, 

 in 1773, conceived a hexagonal prism to be built up 

 by the juxta-position of solid rhombs on the planes 

 of a rhombic nucleus 4 . It is not clear 5 whether 

 Haiiy was acquainted with Bergman's Memoir, at 

 the time when the cleavage of a hexagonal prism of 

 calcspar, accidentally obtained, led him to the same 

 conception of its structure. But however this might 

 be, he had the indisputable credit of following out 

 this conception with all the vigour of originality, 

 and with the most laborious and persevering earnest- 

 ness ; indeed he made it the business of his life. The 

 hypothesis of a solid, built up of small solids, had this 

 peculiar advantage in reference to crystallography ; 

 at rendered a reason of this curious fact ; that a 

 certain series of forms occur in crystals of the same 

 kind, while other forms, apparently intermediate 

 between those which actually occur, are rigorously 

 excluded. The doctrine of decrements explained 

 this ; for by placing a number of regularly-decreas- 

 ing rows of equal solids, as, for instance, of bricks, 

 upon one another, we might form a regular equal- 

 sided triangle, as the gable of a house ; and if the 

 ^breadth of the gable were one hundred bricks, the 



* De Formis Crystallorum. Nov. Act. Reg. Soc. Sc. Ups. 



1773. 



5 Traite de Miner. 1822. i. 15. 



