VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. ]31 



nous ; marble^ chalk, fluor, &c. give a faint light when sprinkled on melted tin 

 just becoming solid. As the temperature of the heater is raised, they continue 

 to give out more and more light. Vitriols of iron, copper, and zinc, previously 

 exsiccated, when thrown on earthen ware or metal made nearly red-hot, give 

 minute flashes of light of momentary duration, such as appear from some of the 

 metallic precipitates, particularly zinc, on a similar treatment ; with this differ- 

 ence however, that the light of most of the precipitates is of a reddish hue. 

 The light of the metals is white, and exactly similar to that of some earths. 



White paper, when dipped in a solution of sal ammoniac, and slowly dried, be- 

 comes black on the heater, and then gives out much less light than common paper. 



If a lump, of the size of a small bean, of fluor, marble, feldspat, or any of 

 the most phosphorescent bodies, be laid on the heater, the light proceeds 

 gradually upwards from the part in contact with the heater, till the whole mass 

 is thoroughly illuminated : if the same piece be heated a second time, it is much 

 less luminous ; nor, if it be broken, are the fragments at all more luminous, 

 either then, or after having been exposed for a month to the iight and sunshine. 

 A little boiling oil at the bottom of a glass flask, when agitated in the dark, illu- 

 minates the whole of the flask. The light of boiling oils proceeds probably 

 from some kind of inflammation, as it is scarcely discernible unless the vessel be 

 agitated; and, if a little oil be thinly spread on the heater, a subtle lambent 

 flame, of a bluish hue, instantly arises. The same thing takes place if horn, 

 bone, hair, saliva, or any animal matter be laid on the heater. 



2. The experiments on the light produced from different bodies by attrition, 

 were chiefly made by rubbing in the dark two pieces of the same kind against 

 each other : all that were tried, with a very few exceptions, were luminous by 

 this treatment. The following is a list of them, arranged in the order of the 

 apparent intensity of their light, and as the lights are either white, or some 

 shade of red, figures are affixed to denote these differences ; (O) denoting a pure 

 white light ; (l), the faintest tinge of red, or flame colour : (2), a deeper shade 

 of red ; (3) and (4), still deeper shades. 



1. Colourless, transparent, oriental rock crystal; and siliceous crystals (O). 

 2. Diamond (0). 3. White quartz; white semi-transparent agate (l). 4. 

 White agate, more opaque (2). Semi-transparent feldspat, from Scotland (2). 

 Brown opaque feldspat, from Saxony (4). Chert of a dusky white, from North 

 Wales (3). 5. Oriental ruby (4). 6. Topaz ; oriental sapphire (O). 7. Agate, 

 deep-coloured, brown and opaque (4). 8. Clear, blackish gun-flint (2). g. 

 Tawny semi transparent flint (3). 10. Unglazed white biscuit earthen-ware (4), 

 1 1. Fine white porcelain (2). 12. Clear, blackish gun-flint, made opaque by 

 heat (3). 13. Flint glass (O). 14. Plate glass; green bottle glass (O). 15. 

 Fine hard loaf sugar (O). 16, Moorstone, from Cornwall (l). Corund, semi- 



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