A New Manual of the Elements of Astronomy, Descriptive and Mathematical

Chapter II. The planets

There are eight large primary planets in the solar system, besides a great number of smaller ones, called MINoR PLANETS, or ASTEROIDS.

The names of the eight large primary planets, in the order of their distances from the sun, are Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

All the primary planets except the earth are divided into two classes, INFERIOR and SUPERIOR PLANETS.

Mercury and Venus are called inferior planets, because they revolve within the orbit of the earth; Mars, Jupiter, Saturn, Uranus, and Neptune are called superior planets, because they revolve beyond the orbit of the earth. Instead of the terms inferior and superior, interior and exterior are sometimes used.

Vulcan.-A planet inferior to Mercury has been supposed to exist; and in 1859, a French astronomer was thought by some to have discovered it. Later observations have not, however, confirmed, but rather disproved, its existence. The name given to this supposed planet is Vulcan.

The MINOR PLANETS are very small planets which revolve around the sun, between the orbits of Mars and Jupiter. Ninety-six have been discovered (1868).

These small planets were at first, and have been, very generally, called Asteroids; they have also been called Planetoids.

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Chapter XII. The Inferior Planets

Mercury ☿

MERCURY is remarkable for its small size, its swift motion, and the great inclination and eccentricity of its orbit. It is, as far as is positively known, the nearest planet to the sun.

a. Name and Sign.-This planet probably derived its name from the swiftness of its motion, Mercury being, in the heathen mythology, the "messenger of the gods." The sign ☿ is supposed to represent the caduceus, or wand, which the god is always seen, in the pictures of him, to carry in his hand,

b. Vulcan.-Reference is made in Art. 16 to a planet supposed by some to exist. between Mercury and the sun; the following are the circumstances connected with its supposed discovery; —On the 26th of March, 1859, a small dark body was seen to pass over a portion of the sun's disc, by M. Lescarbault, a French physician, but an amateur of astronomy; and this appeared to him to indicate the existence of a planet whose orbit must be included within that of Mercury. From the observations which he made with his rude instruments, he calculated its period at about 20 days; its distance, 14,000,000 miles; and the inclination of its orbit, about 12~, On publishing this fact, the celebrated French astronomer and mathematician, Leverrier, visited him, and after closely questioning him as to his means and method of observation, was completely satisfied of the truth of his statements. Singular to say, however, no other observer has been able to detect any indications of such a planet; but, on the contrary, M. Liais, an astronomer of skill and experience, who happened to be engaged in observations of the sun, at Rio Janeiro, at the identical moment of M. Lescarbault's alleged discovery, asserted positively that no planetary object was visible at that time. The existence of any planet inferior to Mercury is therefore considered very doubtful.