VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 367 



avocations and circumstances, have been very mudh interrupted. My acknowledg- 

 ment of obligation to the learned who have made this progress in science, is the 

 best recommendation I can give to others to examine their works. Those whose 

 talents and time are devoted to the investigation of every mineral substance, can 

 have no respite to their labour; minerals, in every state of their formation, per- 

 fection, and decomposition, as they occur in mines, must have their qualities im- 

 mediately ascertained, and be reserved for profit, or thrown away on the heap. 

 The practical miner could not, without external characters, make any progress. 

 The valuable minerals are soon pointed out by assay, and their appearance remem- 

 bered. The accuracy of selection depended, in all periods, much on the ex- 

 perience of the miners. It remained for Mr. Werner to give the utmost degree 

 of accuracy which the irregular external characters can acquire, by fixing appro- 

 priate terms to all the characters which occur, and which the senses can discrimi- 

 nate. In 1774, he opened his system of external characters of minerals, and the 

 perfection he has since given to it, has rendered it very general. The Leskean 

 collection, arranged after Mr. Werner's method, has procured, in Mr. Kirwan, a 

 powerful support to the introduction of that system in this country; and we have 

 already some other valuable publications, to recommend and introduce other 

 favourite systems of the Continent. It is therefore at this time the English mine- 

 ralogist should be invited to examine, if not to prefer, permanent characters, so 

 far as the progress of crystallography has collected them, or at least to give them a 

 distinguished rank among external characters of bodies. 



If prejudice too long has retarded the union of intrinsic and extrinsic characters, 

 it has also occasioned a schism among the advocates of crystallography. Rome 

 de l'lsle, in the year 1772, published the first edition of his Essay on Crystallo- 

 graphy, which he states to be a supplement to Linnaeus; and, by the assistance of 

 a very few friends, he was enabled to increase the number of crystals in a degree 

 to assume the appearance of a system. He told me, that the accuracy of his 

 measurement of angles of minute crystals was the acquirement of great practice, 

 but that the Count de Bourbon, after a short practice, attained equal correctness, 

 and afforded him assistance, which he acknowledges in his 2d edition to have re- 

 ceived, particularly by the discovery of crystals in Dauphine, Auvergne, Franche- 

 Comte, &c. 



The Abbe Hauy, an accurate and patient observer, and a good mathematician, 

 considered crystallography as founded on certain laws, reducible to demonstration 

 by calculation. In the beginning, the differences of Bourguet and Capeller were 

 not more pointed than those of Rome de l'lsle and the Abbe Hauy; but the pro- 

 gress of observation and calculation having demonstrated their mutual utility, the 

 observer and measurer of crystals will now rest satisfied only when calculation con- 

 firms actual measurement. To the Abbe Hauy is also due a late scheme to simplify 

 calculation, by expressing, according to algebraical formulae, the different laws 

 which determine the modifications of crystals. So far as they are the result of cal- 



