M. A. De la Rive on the Cause of Aurora Boreales, 447 



of the globe; from this ring proceeds a conducting rod, which, 

 carefully isolated, traverses the same tubnlure as the iron bar, 

 but without communicating with it, and terminates externally 

 in a knob or hook. When by means of a stop-cock adjusted 

 to the second tubulure of the globe, the air in it is rarefied up 

 to 3 to 5 milHmetres, the hook is made to communicate with 

 one of the conductors of an electric machine, and the external 

 extremity of the iron bar with the other, so that the two elec- 

 tricities unite in the interior of the globe, forming between the 

 internal extremity of the iron bar and the copper ring which 

 is at its base, a more or less regular fascicle of light. But if 

 the external extremity of the iron bar is placed in contact with 

 one of the poles of a strong electro-magnet, taking good care 

 to preserve the isolation, the electric light takes a very different 

 aspect. Instead of issuing, as before, from the different points 

 of the surface of the terminal part of the iron bar, it is emitted 

 only from the points which form the contour of this part, so 

 as to constitute a continuous luminous ring. This is not all : 

 this ring, and the luminous jets which emanate from it, have a 

 continuous movement of rotation around the magnetized bar; 

 one while in one direction, at other times in another, according 

 to the electric discharges and the direction of the magnetiza- 

 tion. Lastly, more brilliant jets appear to issue from this 

 luminous circumference without being confounded with those 

 which terminate on the ring, and form the fascicle. As soon 

 as the magnetization ceases, the luminous phsenomenon be- 

 comes again what it was previously, and what it is generally in 

 the experiment known by the name of the electrical egg. Not 

 having any powerful machine at my disposal, I used for my 

 experiment an Armstrong's hydro-electric machine, the boiler 

 of which I made to communicate with the copper ring, and 

 the isolated conductor which receives the vapour with the iron 

 bar, or vice versa when I wished to change the direction of 

 the discharges. The experiment succeeded very well in this 

 manner. 



The experiment which I have just described appears to me 

 to account very satisfactorily for what passes in the phaeno- 

 menon of the aurora borealis: in fact, the light which results 

 from the union of the two electricities in the part of the atmo- 

 sphere which covers the polar regions, instead of remaining 

 vaguely distributed, is carried by the action of the terrestrial 

 magnetism round the magnetic pole of the globe, whence it 

 seems to rise in a revolving column, of which it is the base. 

 We thus understand why the magnetic pole is always the 

 apparent centre whence issues the light constituting the aurora 

 borealis, or toward which it appears to converge. I shall not 



