49 NOMENCLATURE CHAPTER IV. AND DIMENSIONS OF THE PLANETS. THE SUN DIMENSIONS OF, REAL AND APPARENT. MODES OF MEASUREMENT BY ANGLES. DEGREES, MINUTES, AND HEATING SECONDS. EFFECTS OF THE SUN., LUMINOUS AND But yonder comes the powerful King of Day, And sheds the shining day, that burnish'd plays On rocks, and hills, and towers, and wandering streams, THUS does Thomson, the philosophic poet of the Seasons, speak of the approach and vivifying influence of that splendid body, the Sun,-whose daily return brings with it so much that renders pleasure and benefit to man. We have already given a general view of the relation existing between the different heavenly bodies. The appearances which are presented to the eye of an observer, an enumeration of the classes into which, for the sake of convenience, the heavenly bodies may be divided, and a short exposition of the mode in which E the theory of gravitation is brought to assist us in the comprehension of their motions, were the subjects which then occupied us. We proceed now to consider each of the planets separately, by which means we shall be able to collect the principal facts and circumstances connected with each planet, so far as that can be done without the aid of mathematics, which does not form a prominent feature in our plan. Before proceeding to the consideration of the heavenly bodies separately, it will be convenient to consider the relation which exists between them all, as regards dimension. Fig. 7 represents the comparative sizes of the Moon and planets. By this we shall, of course, be understood to mean, that the twelve circles represented in p. 48, bear the same proportion one to another, as the diameters of the planets bear to one another, respectively. The Sun is so very much larger than any of the planets, that we could not introduce into our figure a circle which would indicate his comparative diameter. This will be rendered evident by the consideration that a circle showing correctly the comparative size of the Sun, must be one hundred and eleven times as large in diameter as the circle representing the Earth. The diameter of the Earth, as we shall hereafter have to show more fully, is about 7920 miles. If now, for the sake of fixing our ideas, we call that quantity 1, then the diameters of the other bodies will be represented by the following numbers : O Sun 24. Jupiter 1⁄2 Saturn. 111.454 10.860 9.987 pre The last four must be considered as approximations to the true proportions; as the diameters of those small. planets have not yet been defined with so much cision as those of the other planets. In astronomical works, these heavenly bodies are frequently expressed by symbols appropriated to them. Before the name of each we have placed the symbol, which distinguishes it among astronomers. The names of the heavenly bodies, before mentioned, are derived from the heathen gods, who also gave their names to such of the metals as were known to the ancients, and likewise to the days of the week. The planets Uranus, Pallas, Juno, Ceres, and Vesta, were not known before the last sixty years. They have all been generally named from the relationship of one deity to the other; the moderns having called the planet discovered by Herschel Uranus, who, in the heathen mythology, was the father of Saturn, who was the parent of Jupiter, of whom Mars was the son. The Moon, called Luna, was said to be the daughter of Terra, the Earth. The characteristics of the planets were also indicated by the known qualities of the deities whose names they respectively assumed. The Earth, being considered as the parent of all created nature, was designated from the goddess whom the ancients invoked to dispense all natural blessings. It formed the centre of their astronomical system, as we have already shown. The planet Mercury, seldom seen, and then but for a short time, resembled "the fleet messenger of the gods." Venus, the most beautiful of all the planets, was the type of the charming goddess of this name. Mars, with its red appearance, showed the wrathful countenance of the god of war. Jupiter, the largest of the planets, resembled the mighty "father of gods and men," while the dim-looking Saturn had its counter-part in the figure of the aged and morose progenitor of Jove. The metals, and the days of the week, which correspond respectively to the Sun, Moon, and five planets, may be seen in the subjoined table. We need not seek to account for the connexion of gold with the Sun, nor of silver with the Moon, when the poets of all ages and nations have celebrated "the golden sun," and "the silvery light of the moon." From iron the god of war formed the weapons of destruction; while the nimble Mercury, that slippery, light-fingered fellow, the patron of roguery throughout the ancient world, was well identified with quicksilver. The metal tin seems to have been assigned to Jupiter, from the circumstance that the Corybantes, the priests of Cybele, who tended the infancy of Jupiter in Crete, used to drown his cries by the clashing of their tin cymbals. Copper is connected with the name of Venus, who was the tutelar deity of the island of Cyprus. This place, where Venus was born, formerly supplied the world with copper from its mines, and honoured Venus above all deities. Lead may have been set down as the type of Saturn, in consequence of the dull, leadlike appearance of that planet. The days of the week were respectively connected with each planet, as each planet was said, according to the old astrological rules, to be in the ascendant for the particular day. We need bring no arguments to show that we are justified in selecting the sun as the first object of our attention :—both from the influence which his superior dimensions enable him to exert on the other planets, and from the vast importance which attaches to him, as the source of light and heat to the other bodies of the solar system. THE SUN. THIS magnificent globe is 883,210 miles in diameter, about 2,774,692 miles in circumference, and distant from the Earth about ninety-five millions of miles. It will be convenient to consider this luminary under three points of view:-1st. His apparent dimensions, as influenced by distance: 2nd. The phenomena presented by him as a source of light :-3rd. The heating effect of his rays. 1. The Sun has but a very small motion in the |