320 HISTORY OF MINERALOGY. 



CHAPTER II. 



EPOCH OF ROME DE LISLE AND HAUY. ESTABLISHMENT OF THE 

 FIXITY OF CRYSTALLINE ANGLES, AND THE SIMPLICITY OF THE 

 LAWS OF DERIVATION. 



WE have already seen that, before 1780, several mineralogists had 

 recognized the constancy of the angles of crystals, and had seen 

 (as Demeste and Werner,) that the forms were subject to modifications 

 of a definite kind. But neither of these two thoughts was so appre- 

 hended and so developed, as to supersede the occasion for a discoverer 

 who should put forward these principles as what they really were, the 

 materials of a new and complete science. The merit of this step 

 belongs jointly to Rome de Lisle and to Hau'y. The former of these 

 two men had already, in 1772, published an Essai de Crystalloc/raphie, 

 in which he had described a number of crystals. But in this work 

 his views are still rude and vague ; he does not establish any con- 

 nected sequence of transitions in each kind of substance, and lays 

 little or no stress on the angles. But in 1783, his ideas 1 had reached 

 a maturity which, by comparison, excites our admiration. In this he 

 asserts, in the most distinct manner, the invariability 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 invari- 

 ability 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 labor 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 in- 

 stance, thirty to calcspar, and sixteen to felspar. He also invented 

 and used a goniometer. We cannot doubt that he would have been 



1 Cristalloyraphie, ou Description de Forties propres a tous les Corps du 

 Rigne Mineral, 3 vols. and 1 vol. of plates. 



2 p. 6S. 3 p. 73. 



