“In ample compass Jove conducts his sphere,
And later finishes his tedious year;
Yet swiftly on his axle turn’d, regains
The frequent aid of day to warm his plains.”
The axis of Jupiter is nearly perpendicular to his orbit, so that he has no sensible change of seasons. This is not the work of chance, as Dr. O. Gregory observes, but wisely ordered by the Divine Architect; for if the axis of this planet were inclined any considerable number of degrees, so many degrees round each pole would be almost six years together in darkness. And as each degree of a great circle on this planet contains more than 700 miles, it is natural to conceive, that vast tracts of land would be rendered uninhabitable by any considerable inclination of his axis.
The appearance of this planet, through a telescope, opens a vast field for interesting inquiry. His surface is not equally bright, but variegated with certain bands, or belts, of a dusky appearance: they run parallel to each other, and are continued round the body of the planet. They are not regular or constant in their appearance: sometimes only one is seen; at other times six or eight. The breadth of them is likewise variable; one belt is sometimes becoming narrow, while another, in its neighborhood, grows broader as if one had flowed into the other: in these cases, an oblique belt has been observed to be between them, as if for the purpose of establishing a communication. Sometimes, one or more spots are formed between the belts, which increase till the whole is united in a large dusky belt. There are also bright spots to be discovered on Jupiter’s surface; these are rather more permanent than the belts, and re-appear after unequal intervals of time. The remarkable spot, by whose motion the rotation of Jupiter upon his own axis was first ascertained, disappeared in the year 1694, and was not seen again till 1708, when it re-appeared exactly in the same place, and has been occasionally seen ever since.
Jupiter is enlightened by four moons, or satellites, each of them larger than that with which we are supplied, and which revolve at different distances from that planet. In the solar system the moons, or satellites, revolve round their respective primary planets as centres, in the same manner as the primary planets revolve round the sun. By means of Jupiter’s satellites, a method has been obtained for demonstrating that the motion of light is progressive, and not instantaneous, as was formerly supposed; which discovery is important to the interests of science. M. Huygens, in his Treatise on Light, concludes from these eclipses, that light transmits itself about 600,000 times faster than sound.
| Revolution. | ||||
|---|---|---|---|---|
| Satellite | Distance. | d. | h. | m. |
| 1st | 250,000 | 1 | 18 | 36 |
| 2d | 401,000 | 3 | 13 | 15 |
| 3d | 648,000 | 7 | 3 | 59 |
| 4th | 1,128,000 | 16 | 18 | 30 |
They are thus referred to by Mallet:
“About him round four planetary moons,