94 SCENERY OF THE HEAVENS. 



vessel to accomplish the circumnavigation of our globe in a year, it would require upwards 

 of ten years to perform at the same rate a similar voyage round Jupiter. His diameter 

 is nearly ninety thousand miles, eleven times that of the earth ; and his volume is thirteen 

 hundred times greater. But as his density is about one-fourth that of the earth, but 

 little exceeding that of water, the quantity of matter in that vast orb is only 331 times 

 greater than what our globe contains. In two years and thirty-five days it would descend 

 upon the sun, if left to the influence of his attraction. 



From the immense velocity of the equatorial regions of Jupiter, and the intensity of 

 the centrifugal force, a considerable deviation in his figure from a perfect sphere is to be 

 expected. This is open to observation. The form of the planet, even on a careless view 

 through a good telescope, appears that of an oblate spheroid. According to the observa 

 tions of Struve and others, while the polar diameter of the earth is only -g-ij less than 

 the equatorial, that of Jupiter amounts to -^, or, in round numbers, his diameter at his 

 poles is six thousand miles less than that at his equator. This ellipticity exceeds that of 

 any of the other planets except Saturn, owing to his great axical speed. The rapid 

 rotation of the planet is a beneficial physical arrangement. Removed to a distance from 

 the source of light and heat which is 5 that of the earth, the sun's apparent size 

 will be TjV what it is to us, supplying to him only -fa of the light and heat that we 

 receive. But before the earth has once rolled round upon its axis, he has accomplished two 

 rotations upon his, and thus his surface is brought under the solar influence after a 

 much shorter interval of suspension than with us, compensating, to some extent, for its 

 diminished power through his distance. That change of seasons which we experience is 

 a diversity unknown to this planet. This arises from the axis being perpendicular, or 

 nearly so, to the plane of the orbit, so that the days and nights are constantly of equal 

 length, and the direction of the sun's rays constantly uniform, oblique towards the poles, 

 and perpendicular at the equator. We have here undoubtedly another instance of wise 

 arrangement, for otherwise the regions towards the poles would have been alternately 

 immersed in the darkness of a six years' wintry night. It is not, however, to be under 

 stood that one uniform season prevails over the surface, but that the same parallels of 

 latitude north and south of the equator enjoy uniformly the same season, whatever that 

 season may be. It is perpetual summer in the equatorial regions, and perpetual winter 

 at the poles; but the rapid rotation of the planet is a security against intense heat 

 accumulating in the former through the invariably direct action of the solar rays, and 

 against the intensity of cold that would prevail at the latter, if their influence was absent 

 for any considerable interval. 



Jupiter, when viewed through a telescope, exhibits a series of zones, or bands, familiarly 

 called belts, stretching across his surface in a direction parallel to his equator, and, 

 generally, to each other. They were first observed at Naples by the Jesuits Zappi and 

 Bartoli, about the year 1633. These belts are variable both in number and breadth. 

 Sometimes eight have been seen, sometimes only one, but more usually three. Instead 

 of being uniformly regular in their shape, they have frequently a lacerated appearance, 

 and, while some continue in the same form for months, others change in a few hours. 

 The aspect of the planet has been sketched by many observers. The views given by 

 Cassini, Dr. Hook, Sir W. Herschel, and Dr. Long are here inserted. In Hook's drawing, 

 taken in May, 1664, a spot appears upon one of the dark belts, by which Cassini ascer 

 tained the period of Jupiter's rotation in the following year. This ancient spot, as it is 

 called, has repeatedly appeared and vanished. It was not seen between the years 1708 

 and 1713, but in the winter of 1834 it was distinctly visible. Other similar spots have 

 been observed, generally situated in the belts. These appearances open a wide field for 

 speculation. The belts have been deemed alterations upon the surface of the planet 



