GEOGNOSTIC PHENOMENA 197 



in Venus. The portion of this planet which is not illumined 

 by the Sun often shines with a phosphorescent light of its own. 

 It is not improbable that the Moon, Jupiter, and the comet8 

 shine with an independent light, besides the reflected solar 

 light visible through the polariscope. Without speaking of the 

 problematical but yet ordinary mode in which the sky is illu- 

 minated, when a low cloud may be seen to shine with an 

 uninterrupted flickering light for many minutes together, we 

 still meet with other instances of terrestrial development of 

 light in our atmosphere. In this category we may reckon the 

 celebrated luminous mists seen in 1783 and 1831 ; the steady 

 luminous appearance exhibited without any flickering in great 

 clouds observed by Rozier and Beccaria ; and lastly, as Arago* 

 well remarks, the faint diffused light which guides the steps 

 of the traveller in cloudy, starless, and moonless nights in 

 autumn and winter, even when there is no snow on the 

 ground. As in polar light or the electro-magnetic storm, 

 a current of brilliant and often coloured light streams through 

 the atmosphere in high latitudes, so also in the torrid zones 

 between the tropics, the ocean simultaneously developes light 

 over a space of many thousand square miles. Here the 

 magical effect of light is owing to the forces of organic nature. 

 Foaming with light, the eddying waves flash in phosphores- 

 cent sparks over the wide expanse of waters, where every 

 scintillation is the vital manifestation of an invisible animal 

 world. So varied are the sources of terrestrial light! 

 Must we still suppose this light to be latent, and combined in 

 vapours, in order to explain Moser's images produced at a 

 distance, a discovery in which reality has hitherto manifested 

 itself like a mere phantom of the imagination. 



As the internal heat of our planet is connected on the one hand 

 with the generation of electro-magnetic currents, and the pro- 

 cess of terrestrial light, (a consequence of the magnetic storm,) it 

 on the other hand discloses to us the chief source of geognostic 

 phenomena. We shall consider these, in their connection 

 with and their transition from merely dynamic disturbances, 



* Arago. on the dry fogs of 1783 and 1831, which illuminated the 

 night, in the Annuaire du Bureau des Longitudes, 1832, pp. 246 and 

 250 ; and, regarding extraordinary luminous appearances in clouds 

 without storms, see Notices sur la Tonnerre, in the Annuaire pour 

 fan 1838, p. 279-285. 



