EPOCH OF DE LISLE AND HAUY. 223 



of the angles of crystals of each kind, under all the 

 changes of relative dimension which the faces may 

 undergo 2 ; and he points out that this invariability 

 applies only to the primitive forms, from each of 

 which many secondary forms are derived by various 

 changes 3 . Thus we cannot deny him the merit of 

 having 'taken steady hold on both the handles of 

 this discovery, though something still remained for 

 another to do. Rome pursues his general ideas 

 into detail with great labour and skill. He gives 

 drawings of more than five hundred regular forms ; 

 (in his first work he had inserted only one hundred 

 and ten; Linnaeus only knew forty;) and assigns 

 them to their proper substances ; for instance, thirty 

 to calcspar, and sixteen to felspar. He also invented 

 and used a goniometer. We cannot doubt that he 

 would have been looked upon as a great discoverer, 

 if his fame had not been dimmed by the more bril- 

 liant success of his contemporary Haiiy. 



Rene-Just Haiiy is rightly looked upon as the 

 founder of the modern school of crystallography; 

 for all those who have, since him, pursued the study 

 with success, have taken his views for their basis. 

 Besides publishing a system of crystallography and 

 of mineralogy, far more complete than any which 

 had yet appeared, the peculiar steps in the advance 

 which belong to him are, the discovery of the im- 

 portance of cleavage, and the consequent expression 

 of the laws of deviation of secondary from primary 

 2 p. 68. 3 p. 73. 



