66. To Mars, our Earth and Moon appear like two Moons, a bigger and a less; changing places with one another, and appearing sometimes horned, sometimes half or three quarters illuminated, but never full; nor at most above a quarter of a degree from each other, although they are 240 thousand miles asunder. [Sidenote: PLATE I. How the other Planets appear to Mars.] 67. Our Earth appears almost as big to Mars as Venus does to us, and at Mars it is never seen above 48 degrees from the Sun; sometimes it appears to pass over the Disc of the Sun, and so do Mercury and Venus: but Mercury can never be seen from Mars by such eyes as ours, unassisted by proper instruments; and Venus will be as seldom seen as we see Mercury. Jupiter and Saturn are as visible to Mars as to us. His Axis is perpendicular to the Ecliptic, and his Orbit is 2 degrees inclined to it. [Sidenote: Jupiter. Fig. I.] 68. JUPITER, the biggest of all the Planets, is still higher in the System, being about 424 millions of miles from the Sun: and going at the rate of 25 thousand miles every hour in his Orbit, as in the circle ♃ finishes his annual period in eleven of our years 314 days and 18 hours. He is above 1000 times as big as the Earth, for his diameter is 81,000 miles; which is more than ten times the diameter of the Earth. [Sidenote: The number of days in his year.] 69. Jupiter turns round his Axis in 9 hours 56 minutes; so that his year contains 10 thousand 464 days; and the diurnal velocity of his equatoreal parts is greater than the swiftness with which he moves in his annual Orbit; a singular circumstance, as far as we know. By this prodigious quick Rotation, his equatoreal inhabitants are carried 25 thousand 920 miles every hour (which is 920 miles an hour more than an inhabitant of our Earth moves in twenty-four hours) besides the 25 thousand above-mentioned, which is common to all parts of his surface, by his annual motion. [Sidenote: His Belts and spots.]