76 HISTOKY OF MINERALOGY. 



peller, who published his Prodromus CrystallograpJiitf, in 

 1723 ; Bourquet, whose Lettres Philosophiques sur la Form- 

 ation de Sels et de Cristaux appeared in 1729 ; and Henkel, 

 the physicus, or naturalist, of the Elector of Saxony, whose 

 Pyritologia is dated 1725. 



This last writer, though his researches are fettered by his 

 literal interpretation of the Mosaic writings, was extensively 

 acquainted with mineral productions, and has given some 

 valuable information on metallic veins. 



Bromel, a French mineralogist, has the honour of being 

 the first (1750) who classified mineral substances according 

 to their pyrognostic qualities, (those induced by the agency 

 of heat,) in combination with their external characters. 

 Cronstedt shortly after applied a mode of classification pre- 

 viously unknown, to which all the characters of mineral sub- 

 stances were submitted, since he was the first who took into 

 consideration their elementary composition. 



It was reserved, however, for Linnaeus to arrange minerals 

 according to their mathematical forms; but though the 

 intuitive sagacity of that great man, observes Professor 

 Whewell, led him to perceive that crystalline form was one 

 of the most definite, and therefore the most important of the 

 characters of minerals, he is conceived to have failed in pro- 

 fiting by this idea ; because in applying it he did not employ 

 the aid of geometry, but was guided chiefly by what appeared 

 to him resemblances, which, however, were arbitrarily selected 

 and often delusive. His efforts led to those of a highly suc- 

 cessful labourer in the same field, Borne de 1'Isle. The great 

 obstacle which lay in the way of these inquiries, consisted in 

 the difficulties presented by the secondary forms of crystals : 

 since, in consequence of the apparent irregularities of these 

 forms, arising from the extension or contraction of particular 

 sides of the figure, each kind of substance may appear under 

 very different forms ; which, however, though apparently 

 dissimilar, are connected with each other by certain geome- 

 trical relations. These may be imagined by conceiving a 

 certain fundamental form, to be cut into new forms, in par- 

 ticular ways. Thus, if we take a cube and cut oif all the 

 eight corners till the original faces disappear, we shall 

 make it an octohedron. This truncation of angles and 

 edges had already been noticed by Demeste; while the 



