Intelligejice and Miscellaneous Articles. 2i5l 



or tile, in the dark, and it shines for a few seconds as a line drawn by 

 a stick of phosphorus upon a wall. This is explained by Professor 

 Draper's hypothesis, in supposing that the chalk had once been at a 

 higher temperature than when used for making the line, under the 

 influence of, or exposed to light, the undulations of which become 

 fixed b)^ the cohesion of the molecules of the chalk consequent on 

 cooling ; and the light, thus fixed within or amongst the molecules, 

 is set at liberty by the high temperature of the heated body on which 

 the line is made, and by completing its undulations becomes visible 

 for the time. But if we prepare some chalk artificially from a solu- 

 tion of lime, by passing carbonic acid gas through it, in a dark 

 room, and carefully exclude all approach of light from the chalk, 

 lines made by this, will give a phosphorescent glow equal to ordinary 

 chalk, and which I think cannot be explained upon the Professor's 

 hj'pothesis, but favours the idea long held, that heat is also a source 

 of phosphorescence. 



The development of the phosphorescence of these lines varies in 

 intensity and duration according to the heat of the body upon which 

 they are made, the hotter the more immediate and brilliant the glow ; 

 whether that has any relation to the quantity of matter abraded I 

 have not determined. It seemed to me, when looking and thinking 

 upon the phaenomenon, as if the force or quantity of heat undulations 

 were retarded and produced a glow of light, the same as when an 

 electric current jjassing through a bad conductor produces ?ieat. 

 This is simply an idea which the experiment suggested, not the result 

 of inquiry. But if heat be a source of phosphorescence as well as 

 light, instead of leading to confusion, as Professor Draper is afraid it 

 will, it may rather serve as a further and an important illustration of 

 the identity of the two forces, heat and light. 



Yours respectfully, 

 198 Pitt Street, Glasgow, James Napieh. 



Feb. 9, 1851. 



ANALYSIS OF TWO SAMPLES OF SOUTH AUSTRALIAN GOLD, 



To the Editors of the Philosophical Magazine and Journal. 



198 Pitt Street, Glasgow, 

 Gentlemen, ^^^- 2^> 1851. 



The following extract from a letter I have received may be inter- 

 esting to some of your readers. 



Yours respectfully, 



James Napier. 



" The gold is found in little thin leaflets amidst cubical crystals of 

 oxide of iron, which is partly mixed with it, so that it cannot be freed 

 entirely by mechanical means. One samijle, freed as much as possi- 

 ble by mechanical means of the oxide of iron, was of specific gravity 

 14"63, and gave by analysis — 



