168 cosMOf. 



able by assuming the existence of an atmosphere partially 

 condensed by strata of clouds, in which, however, the region 

 resting upon the equator is free froru vapor and diaphanous 

 probably in consequence of the trade- winds. Since, as Will- 

 iam Herschel already assumed in a treatise in the 83d vol. 

 of the Philosophical Transactions, which appeared in 1793, 

 the cloud-surface reflects a more intense light than the sur- 

 face of the planet, so that part of the ground which we see 

 through the clearer air must have less light (appear darker) 

 than the strata of clouds reflecting large quantities of light. 

 On that account gray (dark) and clear bands alternate with 

 each other ; the former appear so much the less dark-colored 

 in proportion to the distance from the center, when, the visual 

 radius of the observer being directed obliquely toward the edge 

 of the planet, at a small angle, they are seen through a larger 

 and thicker mass of atmosphere, reflecting more light. 



obsei've daus les pays de montagnes quelque chose J'analogue : quand 

 on se troLive pres d'un foret de sapin, elle parait noii-e ; mais k mesure 

 qu'on s'en eloigne, les couches d'atmo'sphere interposees devienneut de 

 phis en plus epaisses et reflechissent de la lumiere. La difference de 

 teinte entre la foret et les objets voisins diminue de plus en plus, elle 

 finit par se confoudre avec eux, si I'on s'en eloigne d'une distance con- 

 veuable." (From Arago's Reports on Astronomy, 1841.) " It is known 

 that there exist above and below the equator of Jupiter two bands less 

 brilliant than the general surface. If these are examined with a tel- 

 escope, they appear less distinct in proportion as the distance from the 

 center increases, and they even become quite invisible near the edges 

 of the planet. All these appearances may be explained by admitting 

 the existence of an atmosphere of clouds, internipted near the equator 

 by a transparent zone, produced, perhaps, by the trade-winds. The at- 

 mosphere of clouds reflects more light than the solid body of Jupiter. 

 Those parts of him which are seen through the transparent zone would 

 have less biightness than the remainder, and would form obscure bands. 

 In proportion as the distance from the center increases, the visual ray 

 of the observer traverses greater and greater thicknesses of the trans 

 parent zone, in such a way that to the light reflected by the solid body 

 of the planet is added the light reflected by the denser zone. The 

 bands w^ould be, from this reason, less obscure the greater the distance 

 from the center. Finally, at the very edges of the planet's disk, the 

 light reflected by the zone, seen in its greatest thickness, would cause 

 the difference of intensity which existed between the quantities of light 

 reflected by the planet and by the atmosphere of clouds to disappear, 

 and the bands which exist only in virtue of that difference would cease 

 to be visible. Something analogous is observed in mountainous coun- 

 tries ; in the neighborhood of a forest of fir-trees they appear black, 

 but in proportion as the observer removes to a greater distance, the 

 interposed atmospheric strata become thicker and thicker, and reflect 

 light. The difference of tint between the forest and the objects near 

 diminishes more and more, and ends by their being confounded to 

 gather on removing to a sufficient distance." 



