356 PHILOSOPHICAL TRANSACTIONS. [ANNO 17Q8. 



the point of the socket over the pivot. I observed sometimes a similar difference 

 of level in the position of the needle at St. Helena, without being able to account 

 for it. It may be possible, that the dip of the needle is subject to a diurnal varia- 

 tion in its vertical movement. I have perused such publications as have appeared 

 on magnetism for some time past : they state no theory of this obscure science, 

 more rational, or satisfactory, than that left us by the celebrated Halley. 



XIX. On the Corundum Stone from Asia. By the Rt. Hon. Cha. Greville, 



F. R. S. p. 403. 



Having contributed to bring into notice the mineral substance from the East 

 Indies which is generally called Adamantine spar, I beg leave to lay before the e. s. 

 the following account of its history and introduction. About the year 1767 or 

 1768, Mr. Wm. Berry, an eminent engraver of stone, at Edinburgh, received from 

 Dr. Anderson, of Madras, a box of crystals, with information of their being the 

 material used in India, to polish all gems but diamonds. Mr. Berry found that 

 they cut agate, cornelian, &c. ; but in his minute engraving of figures, on seals, 

 &c. the superior hardness of the diamond appeared preferable ; and its dispatch 

 compensated for the price : the crystals were therefore laid aside, as curiosities. Dr. 

 Black ascertained their being different from other stones observed in Europe, and 

 their hardness attached to them the name of Adamantine spar. Col. Cathcart sent 

 me its native name, corundum, from India, with some specimens, given to him by 

 Dr. Anderson, in 1784, which I distributed for analysis. 



When the native name was obtained, it appeared, from Dr. Woodward's Cata- 

 logue of Foreign Fossils, published about 1719, that the same substance had been 

 sent to him from Madras, by his correspondent Mr. Bulkley. In his first Cat. of 

 Foreign Fossils, p. 6, £ 17 ; " Nella Corivindum is found in fields where the rice 

 grows : it is commonly thrown up by field rats, and used, as we do emery, to polish 

 iron." Page 1 1, x 13 ; " Telia Convindum, Fort St. George, Mr. Bulkley. 'Tis 

 a talky spar, grey, with a cast of green : it is used to polish rubies and diamonds." 



In Dr. Woodward's additional Cat. of Foreign Fossils, published in 1725, p. 6, 

 £ 10: " Nella Corivendum is found by digging at the foot or bottom of hills, 

 about 500 miles to the southward of this place. They use it as emery, to clean 

 arms, &c. it serves also to grind rubies, by making it like hard cement, by the help 

 of stick-lac mixed with it. East India. Mr. Bulkley." — These, with a few others 

 in Woodward's Catalogues, are the only instances by which any author, prior to 

 1768, appears to have noticed this substance. 



This information being unsatisfactory, and every appearance of the stone indi- 

 cating it to be part of a stratum, I wrote repeatedly to friends in India, to ascertain 

 if possible, the situation of the rock, and, if near the sea, to send a considerable 

 quantity, as ballast, with a view of applying it to cut and polish granites, porphyry, 

 and other stones, which the high price of cutting and polishing excluded from 

 useful or ornamental work. But my inquiries at Madras were fruitless : by some I 



