JUPITER. 513 



several years in succession exclusively peculiar to the two 

 grey girdles bordering upon the equator, sometimes the north 

 and sometimes the south. The process of spot-formation is, 

 therefore, locally variable. Schwabe's observations, made in 

 November, 1834, likewise show that the spots on Jupiter 

 seen with a 280-fold magnifying power in a Fraunhofer 

 telescope, sometimes resemble the small nucleoid spots sur- 

 rounded by a halo upon thf Sun. But still their darkness is 

 less than that of the satellite shadows. The nucleus is pro- 

 bably a part of the body of Jupiter itself, and if the atmo- 

 spheric opening remains fixed above the same spot, the motion 

 of the spots gives the true rotation. They also separate 

 sometimes, like the Sun-spots, as Dominique Cassini discovered 

 as early as 1665. 



In the equatorial zone of Jupiter are situated two broad 

 principal streaks or girdles, of a grey or greyish-brown colour, 

 which become paler towards the edges, and finally disappear 

 entirely. Their boundaries are very irregular and variable ; 

 both are separated by an intermediate bright equatorial 

 streak. Towards the poles also the whole surface is covered 

 with numerous, narrower, paler, frequently interrupted, even 

 finely branched streaks, always parallel to the equator. 

 48 These phenomena," says Arago, 7 * 4t are most easily explain- 



78 " On sait qu r il existe au-dessus et au-dessous de 1'equa- 

 teur de Jupiter deux bandes moins brillantes que la surface 

 generale . Si on les examine avec une lunette, elles parais- 

 sent moins distinctes a mesure qu'elles s'eloignent du centre, 

 et meme elles deviennent tout-a-fait invisibles pres des bords 

 de la planete. Toutes ces apparences s'expliquent en admet- 

 tant 1' existence d'une atmosphere de nuages interrompue aux 

 environs de 1'equateur par une zone diaphane, produite peut- 

 etre par les vents alises. L'atmosphere de nuages reflechissant 

 plus de lumiere que le corps solide de Jupiter, les parties de 

 ce corps que Ton verra i travers la zone diaphane, auront 



