546 M. A. de la Rive on the Aurora Boreales, 



crystals. On moistening them with hydrochloric acid, with the 

 precautions already indicated, the closest observation could not 

 detect any evolution of gas ; evidently no formation of carbonate 

 of lime had taken place. 



This experiment proves, in the first place, that a solution of 

 hydrate of potash is sufficient to absorb completely the carbonic 

 acid contained in the air ; and secondly, that air which has been 

 carefully and sufficiently heated to redness, and then passed 

 through caustic potash, is and remains free from carbonic acid ; 

 while, on the other hand, air that has not been heated to redness, 

 when passed through the same apparatus and through the same 

 quantity of potash, still yields to potash a distinctly perceptible 

 quantity of carbonic acid, which must therefore have been formed 

 during the passage of the air through the apparatus. 



In conclusion, I cannot omit publicly acknowledging my 

 obligation to Dr. Finkener for the willing aid he afforded me in 

 putting together, in Prof. H. Rose's laboratory, the complicated 

 apparatus required for these experiments. 



LXXV. Further Researches on the Aurora Boreales, and the Phe- 

 nomena which attend them. By M. A. de la. Rive*. 



THE object which I have in view in this new investigation is 

 to show that the theory which I have advanced of the phe- 

 nomenon of auroras boreales is remarkably confirmed by observa- 

 tions made during the last few years, — especially by those of Mr. 

 Walker on the currents exhibited by telegraphic wires, notwith- 

 standing that this learned observer has deduced from them con- 

 clusions unfavourable to this theory. 



I will in the first place call attention to two fundamental points 

 which have been confirmed by observation, and which may now 

 be regarded as definitively established in science. 



The first of these points is the coincidence of the occurrence 

 of auroras boreales and auroras australes ; it has been established 

 by numerous observations made in the two hemispheres, parti- 

 cularly at Hobart Town in the southern hemisphere, and at Chris- 

 tiania in the northern. 



The second important point, likewise definitively established 

 in science, is that the phenomenon of aurora borealis and aus- 

 tralis is an atmospheric phenomenon. Father Secchi and several 

 other distinguished scientific men were of this opinion, which 

 had already been expressed by Arago, and the truth of which I 

 have endeavoured to demonstrate in my former researches, and 

 is confirmed by recent investigations. 



* Extract, communicated by the Author, of a memoir read before la 

 Societe de Physique et d'Histoire Naturelle de Geneve on the 6th of Fe* 

 bruary, 1862. 



