196 EULOGY ON ARTHUR AUGUSTE DE LA RIVE. 



constellatiou Pegasus. The inhabitants of Paris were greatly alarmed. 

 They supposed that some great iuceudiary machine had beeu put in 

 play, to force the walls or demoralize their defenders. A few of them, 

 seeing that it was a remarkable example of the aurora borealis, sought 

 in it such omens, happy or otherwise, as their excited i)atriotism sug- 

 gested. 



The Aurora of the ISTorth, as Gregory of Tours called it thirteen hun- 

 dred years ago, varies somewhat in aspect with the latitude. In the 

 polar regions it is so common that it ceases to excite remark, and is 

 often confounded with the twilight. In the center of Europe it is less 

 frequent, and almost always characterized by the deep bloody hue of 

 the sky, and the rays that dart like lances across it. Its appearance 

 justifies the description that it seems as if two great armies, enveloped 

 in fiery vapor, were engaged in mortal combat. In Calabria, where it is 

 still more rare, the imagination finds in it arcades and porticoes, while 

 Greece, always poetical, and very seldom honored by this celestial vis- 

 itation, sees in the illuminated sky the assembly of the gods in council 

 upon Olympus in the presence of Jupiter. 



How are we to account for these appearances ? Auguste De La Rive 

 considered that they were produced by electrical conflicts, silent and 

 mysterious, converging toward the magnetic pole of the earth. Every 

 one is familiar with the electric light, whose power is exhibited in the 

 light-house, on the stage, and in public illuminations. This brilliant 

 phenomenon, discovered by Davy, was especially noticed by Arago, 

 who declared, «j)rion, that it would oflerthe then strange spectacle of a 

 flame obeying the action of a magnetic bar. Experiment confirmed his 

 prediction. When this luminous arch is approached by the poles of a 

 strong magnet, it is attracted or repulsed ; its curvature increases, the 

 brilliancy of the flame diminishes ; it is varied by jerks and by flashes 

 of colored light when silk is rubbed near it, and the arch at last breaks, 

 when the curvature is so gTeat that it extends too much the surface 

 passed over by the electrical discharge. A magnetic needle placed in 

 the vicinity manifests, by its incessant agitation, that it is aflected by a 

 strong magnetic influence. Is not this the image of the aurora polaiis 1 



Arago devoted many years to the study of the influence of the aurora 

 borealis upon the magnetic needle; and often announced the appear- 

 ance of the phenomenon in the north of Europe, even before it was 

 manifested in France. He was too cautious, however, to hazard an 

 opinion in regard to its nature. Auguste De La Rive took up the sub- 

 ject — we should rather say, devoted himself to it — and among the many 

 reasons for regretting the death of this illustrious savant is the loss to 

 science of a work he was preparing uiK)n the polar lights, the materials 

 for which he had spared no pains in collecting. The apparatus is well 

 known, at least in the lecture-room, bj- means of which he reproduced 

 the fundamental conditions of the phenomenon, which he considered 

 due to the formation of a luminous ring in the upper regions ot the 



