Page:The fairy tales of science.djvu/216

180 clearly denoting the existence of large masses of snow. The climate of this planet must be considerably colder than ours; but, from the similar obliquity of the ecliptic, and almost identical period of diurnal rotation of the two, the changes of the seasons must be very similar to our own, though with much greater variations.

Besides these larger planets, there are found between Mars and Jupiter about thirty smaller planets and asteroids, most of them exceedingly minute, and discernible only through the telescope. Vesta and Pallas are the brightest among them, and may, when nearest to us, be just barely detected with the naked eye, though even then with the greatest difficulty only.

To convey to the mind of the reader an intelligible general impression of the relative magnitudes and distances of the principal parts of the planetary system, let a globe two feet in diameter be placed on a well levelled field, to represent the Sun. Mercury will then be represented by a grain of mustard-seed on the circumference of a circle 164 feet in diameter for its orbit. Venus will appear as a pea, on a circle 284 feet in diameter; the Earth of the same size, on a circle of 430 feet; Mars of the size of a rather large pin’s head, on a circle of 654 feet; Juno, Ceres, Vesta, and Pallas, grains of sand, in orbits of from 1000 to 1200 feet; Jupiter a moderate-sized orange, on a circle about 720 yards across; Saturn a smaller orange, on a circle of four-fifths of a mile; Uranus a small plum, on the