Prof. Potter on the Aurora Boreales. 5 1 



Chloride of rubidium . . . 59*80 



Chloride of potassium . . . 13*35 



Chloride of sodium 1 oa-S^ 

 Chloride of lithium j 



100*00 



Although the salt remaining in the mother-liquor contains, as 

 the preceding analysis shows, about 60 per cent, of chloride of 

 rubidium, a preliminary separation by crystallization is not ad- 

 visable, as the salt which crystallizes out contains nearly half the 

 total quantity of chloride of rubidium, thus rendering necessary 

 a repetition of the complete series of platinum precipitations, and 

 tedious washings with boiling water. 



Heidelberg, March 1862. 



IX. Observations upon a Paper by M. De la Rive "On the 

 Aurora Boreales" in the Supplement to the Philosophical Maga- 

 zine for June 1862. By Professor Potter, A.M.* 



IN his paper entitled " Further Researches on the Aurorse 

 Boreales, and the Phenomena which attend them/' M. J>e 

 la Rive assumes that the meteor is an atmospheric and terres- 

 trial result only. If he had first studied the locality of the phe- 

 nomena, I have no doubt he would have given us a valuable 

 paper, from his great knowledge of the science of electro- 

 magnetism ; but he unfortunately follows the old Aristotelian 

 view, that the meteor is terrestrial and atmospheric, and ignores 

 the scientific principle that inaccessible heights and distances 

 can be only measured by parallactic observations with the aid of 

 trigonometry. 



The reasonings and measurements of H alley f, Cavendish J, 

 Bergman, Dalton§, and others have given the locality of the 

 meteor as beyond the earth's atmosphere, and its height from 

 52 miles the lowest, calculated by Cavendish, to very great 

 heights. 



At the Meeting of the British Association at Cambridge in 

 1833, after I had read a paper on the height of the Aurora of 

 March 21st, 1833 1|, and a discussion which followed, a com- 

 mittee was appointed to direct observers, collect observations, 

 and settle the discordant opinions on the subject of the locality 

 of the meteor. Only one hurried meeting of a few of the com- 

 mittee was held at Cambridge, at which Dalton was not present ; 



* Communicated by the Author. 



f Phil. Trans, for 1716. + Ibid. 1790. 



§ Meteorology, 2nd edition, p. 227; and Phil. Trans. 1828. 

 H See Phil. Mag. for December 1833. 



E 2 



