[ 183 ]
LXXVI. Iron, however, being harder in its Texture than Stone, will cut ſuch as are both harder and more ſolid than theſe.
LXXVII. There ſeems, however, yet an Abſurdity in this, ſince the Whetſtone has Power upon, and takes off a Part of the Iron Inſtruments which are ſharpened on it, and the Inſtrument may be made to cut and work upon the Whetſtone; but notwithſtanding,
mond-powder is the great Thing in Uſe with us on theſe Occaſions, and next to it Emery; and Emery was alſo known to the Antients, and uſed by them on the ſame Occaſions. Σμίρις λίθος ἐϛὶν ᾗ τὰς ψήφȣς οἱ δακτυλιογλύφοι σμήχȣσιι. Dioſcorides. Σμίρις ἄμμȣ εἶδος, ᾗ σμήχονται σκληροὶ τῶν λίθων. Heſychius.
Cardanus imagines, but erroneouſly, that the Porus of the Antients was our Emery; or elſe, that our Emery was unknown to them; which is no leſs an Error: For it is evident, they were well acquainted with its Uſes. And as to what he adds, of their working on Gems with the Porus, and Fragments of the Lapis Obſdianus, Salmaſius, who had certainly read more than moſt Men, affirms, he never could find any Account of it among them. Pliny relates, indeed, that Fragments of the harder Kind of the Oſtracites were uſed for this Purpoſe; lib. 37. c. 10. Oſtracia ſeu Oſtracites eſt teſtacea durior: altera Achatæ ſimilis niſi quòd Achates politura pingueſcit; duriori tanta ineſt vis ut aliæ gemmæ ſcalpantur fragmentis ejus. And that a Sand prepared from the Porus, was uſed for poliſhing Marble, but not Gems; Craſſior enim harena laxioribus ſegmentis terit, & plus erodit marmoris, majuſque opus ſcabritie polituræ relinguit. Rurſus Thebeicia polituris accommodatur, & quæ fit e poro lapide aut e pumice. For poro lapide, many of the Copies have toro lapide, and duro lapide; but the concurrent Accounts of other of the Antients determine it to be this particular Stone that is meant. And the ſame Author expreſsly ſays,
