4!4!6 M. A. De la Rive on the Cause of Aurorce Boreales. 



modification of the atomic constitution of glass, I shall be 

 content to have brought the subject before the British Asso- 

 ciation : if these observations, on the contrary, are considered 

 not worthy of the importance I attach to them, I shall have 

 my excuse in the love of an art to which I have all my life 

 been zealously devoted. , 



LV. On the Cause of Aurorae Boreales. By Auguste de 

 LA Rive, being an Extract from a Letter to M. Regnault*. 



I HAVE just read, in a memoir by M. Morlet on the 

 Auroras Boreales, inserted in the Annates de Chiniie et de 

 Physique, 3rd series, vol. xxvii. the following passage : — 



*' With regard to the origin of this luminous matter (that 

 of the aurora borealis), it seems natural to attribute it to the 

 electric fluid contained in the atmosphere, and which, at great 

 heights where the air is rarefied, must become luminous as 

 under the receiver of the air-pump and in the barometric 

 vacuum : this hypothesis would acquire a great probability if 

 we succeeded in proving, by direct experiments, that mag- 

 netism exerts an influence on electric light." 



This last expression induces me to request you to have the 

 goodness to communicate to the Academy of Sciences an ex- 

 periment which I mentioned to you on my passage through 

 Paris last June, and which you may perhaps remember ; its 

 object was to show, in support of the theory which I had ad- 

 vanced of the aurora borealis, the influence exerted by mag- 

 netism upon the light which is produced in ordinary elec- 

 tric discharges. Hitherto this influence has only been shown 

 in the case of the luminous arc which escapes between two 

 conducting points, each communicating with one of the poles 

 of a voltaic battery; which is very different, both as con- 

 cerns the phaenomenon itself, and in what concerns its ap- 

 plication to the theory of the aurora borealis. The following 

 is my experiment. 



I introduce into a glass globe about SO centimetres in dia- 

 meter, by one of the two tubulures with which it is furnished, 

 a cylindrical iron bar, of such length that one of its extremities 

 reaches nearly to the centre of the globe, whilst the other 

 extends from 3 to 4 centimetres out of the tubulure. The 

 bar is hermetically sealed in the tubulure, and covered through- 

 out its length, except at its two ends, with an isolating and 

 thick layer of wax. A copper ring surrounds the bar above 

 the isolating layer in its internal part the nearest to the side 



* From the Comptes Rendus for Oct. 15, 1849. 



