340 Baron Humboldt on the Luminonsness of the Earth 



process. The intensity of the earth-light, or rather the degree 

 of luminosity which it diffuses, exceeds by a little, in the case 

 of the brightest coloured rays that shoot up to the zenith, the 

 light of the moon in her first quarter. Occasionally, as on the 

 7th of January 1831, a printed page can be read without 

 straining the sight. This light-process of the earth, which the 

 Polar regions exhibit almost incessantly, leads us by analogy 

 to the remarkable phenomenon which the planet Venus pre- 

 sents. The portion of this planet which is not illuminated by 

 the sun, glows occasionally with a proper phosphorescent gleam. 

 It is not improbable that the moon, Jupiter, and comets, be- 

 sides the reflected sun-light recognisable by the polariscope, 

 also emit light produced by themselves. Without insisting 

 on the problematical, but very common phenomenon of sheet- 

 lightning, in which the whole of a deep massy cloud is flicker- 

 ingly illuminated for several minutes at a time, we find other 

 examples of terrestrial evolutions of light. To this head be- 

 long the celebrated dry -fogs of 1783 and 1831, which were lu- 

 minous by night ; the steady luminousness of large clouds, 

 perfectly free from all flickering, observed by Rozier and Bec- 

 caria ; and even the pale difi^used light, as Avago has well ob- 

 served, which serves to guide us in the open air, in thick- 

 ly clouded autumn and wintry nights, when there is neither 

 moon nor star in the firmament, nor snow vipon the ground. 

 As in the phenomenon of the Polar light occurring in high 

 northern latitudes, in other words, in electro- magnetic storms, 

 floods of flickering, and often party-coloured light stream 

 through the air ; so in the hotter zones of the earth, between 

 the tropics, are there many thousand square miles of ocean 

 which are similarly light-engendering. Here, however, the 

 magic of the light belongs to the organic forces of nature. 

 Light-foaming flashes the bursting Avave, the wide level glows 

 with lustrous sparks, and every spark is the vital motion of an 

 invisible animal world. So manifold is the source of terrestrial 

 light. And shall we conceive it latent, not yet set free in va- 

 pours, as a means of explaining Moser's/;«c^w/'^5, — a discovery in 

 which reality still presents itself to us as a vision shrouded in 

 mystery \ — Kosmosy s. 206, and Cosmos, English edition, p. 209. 



