453 On the Non-polarization of the Aurora Borealis. 



purities, which in the greater part of the other metals often deter- 

 mines whether the specimen tested is repelled or attracted. 



On comparing the oxides and chlorides of the magnetic metals 

 with those of the diamagnetic metals given, I find that there are 

 three oxides and three chlorides of the magnetic metals all 

 coloured ; of the diamagnetic metals, there are three white oxides 

 and one coloured, and four white chlorides* and one coloured, 

 showing a great preponderance of white compounds to the dia- 

 magnetic substances. 



Chlorine being a diamagnetic body, might be expected to give 

 a greater proportion of colourless bodies among the chlorides 

 than oxygen among the oxides of the same metals. To ascertain 

 if this was so, I selected thirty-six of the metals which have 

 been most examined, and tabulated their chlorides and oxides : — 



Of the oxides, twenty-four were coloured and twelve white ; 



Of the chlorides, nineteen were coloured and seventeen white. 



The chlorides, in conformity with this view, are found to fur- 

 nish more white compounds than the oxides. 



LXXII. Non-jiolarization of the Aurora Borealis. By William 

 John Macquorn Rankine. C.E., F.R.S.E., F.R.S.S.A., ^c. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



ALTHOUGH the results which I have obtained are purely 

 negative, it may be useful to record the fact, that having 

 on several occasions during the last eight months examined the 

 light of the aurora borealis with a Nicholas pi'ism, I have never 

 detected any trace of polarization. To show that this did not 

 arise fi-om the faintness of the light, I may mention, that on the 

 last occasion when I observed it, the polarization of the same 

 light produced by reflexion from the surface of a river was 

 distinctly visible, although the direct light was evidently free 

 from all sensible polarization. 



This fact is adverse to the supposition that the light of the 

 aurora borealis is reflected from crj^stals of ice. 

 I am. Gentlemen, 



Your most obedient Servant, 

 Glasgow, Nov. 22, 1852. W. J. M. Rankine. 



* One of these is a bichloride. 



