Corundum Stone from Afia,— -Singular Lunar Halo. 485 



The corundum of China, 



Argillaceous earth - » « » 



Siliceous earth . - • - 



Oxide of iron ■ . - - 



. Lofs - - •> > ^ . 



That the analyfis of fapphire of Mr. Klaproth may be compared, it is here added. 

 Argillaceous earth - - - - 98 50 



Calx of iron - - - - . 10 



Calcareous earth - • * - o 50 



100 



Iron-ore cryftalllzed is often mixed with the Chincfe corundum, as I have before ftatcd, 

 and may be confidered as accidentally interpofed, not combined. In the corundum of the 

 coaft, the greenifli colour may indicate the combination of iron, as the blue colour does in 

 the fapphire ; and the proportion of iron in both is nearly alike. 



There, then, is the ~ — ^-^ and i- of filex in corundum, evidently an integral 



100 100 ' * 



part of the coarfe corundum cryftal, and not of the fapphire ; but it y/\\\ require an analyfis 



of the vitreous or pellucid corundum to decide that filex is a conftituent part of corundum : 



there will then remain to account for the calcareous earth ; and, having eftabliflied its being 



a conftituent part of the fapphire, the fmall proportion of ■ cannot be expefted to 



produce a very notable difference. 



It is not neceflary to do more than thus to hint at what further analyfis and examination 

 of former experiments are required, to afcertain the analogy or identity of the fapphire and 

 oriental ruby with corundum. 



I have before ftated, that I have corundum (which has the fame texture and frafture as 

 the common colourlefs corundum) of a ruby red, and alfo of fapphire blue, and of fapphire 

 blue and white colours. 



I have fapphires yellow and blue, white and blue, brown and greenifli, and of a purplifli 

 hue ; thefe I fliould confider as corundum, with fratSture of vitreous luftre. 



(To be continued.) 



II. 



Jin Account of aftngular Halo of the Moon. In a Letter from WiLLIAM Hall, Efq. of 

 Whitehall, F.R.S. Edin. to Sir James Hall, Bart. F.R.S. Edin.* 

 DEAR SIR JAMES, Whitehall, near Berwick, April 2, 1796. 



I 



SEND, under cover, tlie reprefentation of a very fingular halo of the moon (pi. XXII. 

 fig. 25.) feen here on the night of the i8th of February laft, about ten o'clock ; and this I 



* Edinburgh Tranfaa';ons, vol. IV. page 173. 



Vol. II. — Ffb. i 799. 3 R have 



