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portions, of a greenish tint, are considered to be bodies of water. The proportion of land to water on the earth is reversed in Mars. "Here every continent is an island; there every sea is a lake: but these, like our own continents, are chiefly confined to one hemisphere, so that the habitable area of the two globes may not differ so much as the size of the planets." The ruddy color of the planet is thought by Herschel to be due to an ochrey tinge in the soil; by others it is attributed to peculiarities of the atmosphere and clouds. Lambert suggests that it is the color of the vegetation, which, on Mars, may be red instead of green. There are constant changes going on in the brightness of the disk, owing, it is supposed, to the variation of the clouds of vapor in its atmosphere. No mountains have yet been discovered. In the vicinity of the poles are brilliant white spots, which are considered to be masses of snow. The "snow zones" apparently melt and recede with the return of summer in each hemisphere, and increase on the approach of winter. We can thus from the earth watch the formation of polar ice and the fall of snow—in fact, all the vicissitudes of the seasons on the surface of a neighboring planet.
THE MLNOK PLANETS.
/ Discovery.—Beyond Mars there is a wide interval which until the present century was not filled. The bold, imaginative Kepler conjectured that there was a planet in this space. This supposition was corroborated by Titius's discovery of what has since been known as Bode's law.
Take the numbers 0, 3, 6, 12, 24, 48, 96, 192, 384, each of which, after the second, is double the preceding one. If we add 4 to each of these numbers, we form a new series:
4, 7, 10, 16, 28, 52, 100, 196, 388.
At the time this law was discovered, these numbers represented very nearly the proportionate distance from the sun of the planets then known, taking the earth's distance as ten, except that there was a blank opposite 28.* This naturally led to inquiry, and a systematic effort to solve the mystery. On the 1st day of January, 1801, the nineteenth century was inaugurated by Piazzi's discovery of the small planet Ceres, at almost the exact distance necessary to fill the gap in Bode's series. This was soon followed by the announcement of other new planets, until (1870) there are one hundred and twelve, and a probability of many more. Indeed, Leverrier has calculated that there may be perhaps 150,000 in all
Description.—These minor worlds, or "pocket planets," as Herschel styled them, are extremely diminutive. The largest of them is Pallas, whose diameter is perhaps 600 miles. Those recently discovered are so small that it is difficult to decide which is the smallest. A French astronomer recently remarked concerning them, that a "good walker could easily make the tour of one in a day;" a prairie farmer would need to pre-empt a whole one for a flourishing cornfield. They all revolve about the sun in regular orbits, comprising a zone about 100,000,000 miles in width. Their paths are variously inclined to the ecliptic; Massilia's 41"', while that of Pallas rises 34°.
Origin.—One-theory concerning the origin of these small planets is, that they are the fragments of a large planet which, in a remote antiquity, has been shivered to pieces by some terrible catastrophe. "One fact seems above all others to confirm the idea of an intimate relation between these planets. It is this: if their orbits consisted of solid rings, they would be found so entangled that it would be possible, by taking up any one at random, to lift all the rest." Another theory is given under the "Nebular Hypothesis."
Names and signs.—Ceres, the first discovered, received the symbol V, a sickle. This was appropriate, since that goddess was supposed to preside over harvests. Pallas, the second, named from the goddess of wisdom and scientific warfare, obtained the sign i, the head of a spear. To Juno, the third planet, was assigned e, a sceptre surmounted with a star, the emblem of the queen of heaven. An altar with fire upon it, ft, appropriately represented Vesta, the household goddess, whose sacred fire was kept burning continually. In, this way names of goddesses and appropriate symbols were used to designate the minor planets which were earliest discovered. Since then a simple circle with the number inclosed has been adopted; thus CD represents Ceres—® is the sign of Pallas.
The king of the gods. Sign 2X, a hieroglyphic representation of an eagle "the bird of Jove."
Description.—From the smallest members of the solar system we now pass at once to the largest planet—the colossal Jupiter. Its peculiar splendor and brilliancy distinguish it from the fixed stars, and vie even with the lustre of Venus. It is one of the five planets discovered in primitive ages. In those early times, Jupiter was supposed to be the cause of storm and tempest. Pliny thought that lightning owed its origin to this planet. An old almanac of 1368, foretelling the harmless condition of Jupiter for a certain month, says, "Jubit es hote and moyste and does weel til al thynges and noyes nothing."
Motion In Space.—Jupiter revolves about the sun at a mean distance of 475,000,000 miles. His orbit has much less eccentricity than those of the smaller planets. Were his path very elliptical, the attraction of the sun would be insufficient to bring him back from its extreme limit, and the huge unwieldy planet would plunge headlong into space. This careful fitting, whereby the plan is always modified to accomplish an end, is everywhere characteristic of nature, and is a continued revelation of its common Author. The revolution of Jupiter among the fixed stars is slow and majestic, comporting well with his vast dimensions and the dignity conferred by four attendant worlds. He advances through the zodiac at the rate of one constellation yearly; so that if we locate the planet now, a year hence we can find it equally advanced in the next sign. Yet slowly as he seems to travel through the heavens, he is bowling along through space at the enormous speed of 500 miles per minute. The Jovian day is only equal to about ten of our hours, while his year is lengthened to about 12 of our years, comprising near 10,000 of his days.
Distance From Earth.—Once in thirteen months Jupiter is in opposition, and his distance from the earth is measured by the difference of the distances of the two bodies from the sun. At the expiration of half this time he is in conjunction, and his distance from us is measured by the sum of these distances.