432 On Mr. Hume's Paper on Barytes. [Dec. 



the appearances of the Aurora, by supposing them produced by the 

 •magnetic fluid which he conceived to be constantly issuing out of 

 the earth, and entering into it in lines, which he thought coincided 

 with the position of the beams of the Aurora Borealis. 



What the nature of the beams or of the cylinders is which con- 

 stitute the Aurora Borealis, we have no means of knowing ; neither 

 can we explain the origin of the light which renders them luminous, 

 though it would appear to be connected with electricity ; but that 

 these cylinders are magnets cannot be for a moment doubted. At 

 present we know only three bodies capable of assuming magnetic 

 properties ; namely, iron, nickel, and cobalt. That the beams of 

 the Aurora Borealis should consist of particles of any of these 

 metals is too monstrous a supposition to be for a moment believed. 

 At the same time, when we call to mind the luminous meteors 

 which are occasionally seen at vast heights above the surface of the 

 earth, and the stony bodies which there is every reason to believe 

 occasionally fall from these meteors, the conjecture, that bodies 

 similar in their nature to some of the solid bodies which constitute 

 our globe may exist in some unknown state in the atmosphere, will 

 not appear altogether extravagant. 



Article VI. . 



Remarks an Mr. Hume's Paper on Barytes, contained in the Philo- 

 sophical Magazine, vol. xiv. 1802. By Mr. R. Phillips. 



Having had occasion to consult various authorities respecting 

 the chemical properties of barytes, I was much surprised on reading 

 the contents of a paper on the subject by Mr. Hume, printed in 

 the Philosophical Magazine for 1802, but which I do not remember 

 to have seen until very lately. 



In this memoir some facts are stated, which the author says he 

 " had never yet seen pointed out by any chemical writers ; " and 

 others are mentioned, which he asserts had never been previously 

 " enumerated by any author." 



The statements which I shall first notice are, " that nitrate of 

 barvtes, not in crystals only, but even a saturated aqueous solution, 

 is perfectly insoluble in nitrous acid of the usual specific gravity; " 

 and " that muriate of barytes is virtually insoluble in muriatic 

 acid." 



Now that these facts were well known, and had been described 

 previously to the publication of Mr. Hume's paper, will appear by 

 the following quotation from a memoir by Sage, contained in 

 vol. lxxxviii. p. M"), of the Memoires de l'Acadcmie des Sciences 

 for 1/SSS : — " L'acide nitreux. a trente deux degres, fait d'abord 

 une vive effervescence avec le '-path pesant acre- : le nitre qui en 



