82 



upon an accurate definition, with a view to facilitate an appropriate 

 denomination. According to this definition they are " Celestial bodies 

 of a small or a very small size, which move in orbits of no very great 

 excentricity round the sun, the planes of which may be inclined to 

 the ecliptic in any angle whatsoever : their motion may be direct 

 or retrograde ; and they may or may not have very considerable at- 

 mospheres, or very small comas or nuclei." 



Description of the Corundum Stone, and its Varieties, commonly known 

 by the Names of Oriental Ruby, Sapphire, &c. ; with Observations 

 on some other Mineral Substances. By the Count de Bournon, F.R.S. 

 Read March 25, 1802. \Phil. Trans. 1802, p. 233.] 



In a former paper, printed in the Philosophical Transactions for 

 the year 1798, Count de Bournon gave an analytical description of 

 the crystalline forms of corundum from the East Indies and from 

 China. From a note inserted at the beginning of the present com- 

 munication, we learn, that the great number of specimens of that 

 substance, since collected from different parts, chiefly of the East, 

 have added so considerably to our knowledge relating to that sub- 

 ject, as to render it necessary not only to correct, but even, in many 

 respects, to alter our opinion concerning it : and that hence, rather 

 than create intricacy by introducing this additional knowledge in the 

 form of a supplement, he had thought it expedient to collect all the 

 information that could be obtained into one point of view, in hopes 

 of delivering, in the present paper, with the addition of a chemical 

 analysis which we are taught to expect from Mr. Chenevix, a com- 

 plete mineralogical history of this curious substance. 



The paper is prefaced by a short historical account of the opinions 

 of former naturalists concerning the corundum stone, and its classi- 

 fication in the mineral system. The first of these, who derived their 

 knowledge chiefly from lapidaries, had no hesitation in placing it 

 among the gems, the hardest of which they distinguished by the 

 epithet Oriental, and subdivided them according to their colours. 

 Rome de Lisle was the first who deduced distinctive characters from 

 the crystalline forms of the different sorts, rejecting the colour as a 

 fallacious character. The first chemists who undertook to analyse 

 this stone, thought themselves authorized to consider it as consisting 

 of new elementary earths ; but afterwards it was thought, and it 

 appears now with much reason, to belong to the class of those stones 

 which are chiefly, if not entirely, composed of argill. Werner at 

 length also undertook the analysis ; but he retrograded somewhat 

 from what has been since found to be the truth, by placing it between 

 pitch-stone and felspar. Abbe Hauy at length, recurring again to 

 the crystalline form, placed it immediately after felspar, and before 

 the Ceylonite ; from both which, however, it differs widely, both by 

 its hardness and specific gravity. 



We are greatly indebted to the zeal and perseverance of our 

 honourable member, Mr. Charles Greville, for a very ample collec-. 



