JUPITER WITHOUT HIS SATELLITES. 
249 
in this respect, but even Saturn is but half as large as Jupiter. 
In mass, this superb planet is not merely <c facile princeps,” but 
exceeds much more than twofold all the other planets taken 
together. We may view, indeed, in Jupiter and his system, a 
miniature, but instead of being >a miniature of our earth, it is 
as a miniature of the whole solar system that he is to be regarded. 
The sun himself, does not so greatly exceed Jupiter in volume 
as Jupiter does our earth. And the bodies which circle round 
Jupiter travel with velocities comparable with those of the 
swiftest members of the solar system. While Mercury and Venus 
travel 100,000 and 80,000 miles an hour, and our earth travels 
68,000 miles an hour round the sun, Jupiter’s inner satellite 
travels upwards of 40,000 miles an hour around its primary. 
Mars travels 55,000 miles an hour round the sun, the second 
satellite travels 32,000 miles an hour round Jupiter. Jupiter 
himself sweeps less swiftly round the sun than these satellites do 
around him, so that through a portion of their orbits they are 
actually retrograding. The third satellite also travels so 
swiftly round Jupiter, as to be reduced very nearly to absolute 
rest when its velocity acts in a contrary direction to that of 
Jupiter. The fourth satellite travels less swiftly than the third, 
but yet as swiftly as the planet Saturn in his orbit around the 
sun. 
Nearly every celestial object has an interest attaching to it, 
other than that derived from its physical aspect, — an interest 
which may be called historical. In the moon, for instance, we 
see an object without which (it is not too much to say) astronomy 
would never have approached its present state of exactness and 
accuracy. Mars, in like manner, afforded evidence such as no 
other planet could supply, when Kepler was engaged in the 
series of researches which rendered his name illustrious, and 
without which Newton’s views might never have been directed to 
gravitation as a universal principle. Venus is connected with 
the determination of the fundamental element of all astronomical 
measures, — the sun’s distance from the earth. Mercury, Saturn, 
Uranus, and Neptune, the sun, fixed stars, comets, asteroids, and 
nebulse, all have their historical interest, derived from the evi- 
dence which they have afforded on special questions of interest. 
Jupiter is second to none in this respect. At a critical period 
in the history of astronomy, when the world of science was 
divided on the subject of the Copernican Theory of the Universe, 
and when all without the world of science were steadfastly opposed 
: to the new views, the discovery that Jupiter was the centre of a 
miniature-system, circling around him as the theory in dispute 
taught that the planets circled around the sun,- — came oppor- 
tunely as an illustration, and to those who could grasp the 
I significance of the phenomenon, as a proof, of the views of the 
