PRELUDE TO THE EPOCH OF DE LISLE ASTD H^UY. 319 



greatly the study of the angular form of crystals might become 

 interesting, and fitted to extend the sphere of our mineralogical know- 

 ledge, I have followed them in all their metamorphoses with the most 

 scrupulous attention." The views of Linnaeus, as to the importance of 

 this character, had indeed been adopted by several others ; as John 

 Hill, the King's gardener at Kew, who, in 1777, published his Spatho 

 r/otcsia ; and Grignon, who, in 1775, says, "These crystallizations 

 may give the means of finding a new theory of the generation of crys- 

 talline gems." 



The circumstance which threw so much difficulty in the way of 

 those who tried to follow out his thought was, that in consequence of 

 the apparent irregularity of crystals, arising from the extension or 

 contraction of particular sides of the figure, each kind of substance 

 may really appear under many different forms, connected with each 

 other by certain geometrical relations. These may be conceived by 

 considering a certain fundamental form to be cut into new forms in 



O 



particular ways. Thus if we take a cube, and cut off all the eight 

 corners, till the original faces disappear, we make it an octohedron; 

 and if we stop short of this, we have a figure of fourteen faces, which 

 has been called a cubo-octokedron. The first person who appears dis- 

 tinctly to have conceived this truncation of angles and edges, and to 

 have introduced the word, is Demeste; 13 although Wallerius 14 had 

 already said, in speaking of the various crystalline forms of calcspar, 

 " I conceive it would be better not to attend to all differences, lest we 

 be overwhelmed by the number." And Werner, in his celebrated 

 work On the External Characters of Minerals, had formally spoken 

 of truncation, acuatign, and acumination, or replacement by a plane, 

 an edge, a point respectively, (abstumpfung, zuschdrfung, zuspitzung,} 

 as ways in which the forms of crystals are modified and often dis- 

 guised. He applied this process in particular to show the connexion 

 of the various forms which are related to the cube. But still the 

 extension of the process to the whole range of minerals and other 

 crystalline bodies, was due to Rome de Lisle. 



18 Lettres, 1779, i. 48. " Sy sterna Miner alogicum, 1772-5, i. 143 



" Leipzig, 1774. 



