QUESTIONS.

What is the appearance of the planet Mars? At what distance from the sun, and in what time does Mars revolve round that luminary, and at what rate of motion? In what time, and at what rate, does Mars turn round its own axis? What quantity of light and heat does he receive from the sun in proportion to what the earth does? Has Mars any moon attending him? What appearances of figure does Mars present at different times? What spots have been observed upon the surface of Mars? In what respects does Mars resemble the earth? How is Jupiter situated from the sun? What are the size and brightness of Jupiter, and what peculiar appearances are observed upon his disc? How many moons attend Jupiter? What are the respective distances of Jupiter's satellites from his body, and what are their times of revolution? At what distance from the sun, and in what time, and at what rate, does Jupiter revolve round him? In what time, and at what rate does Jupiter revolve round his own axis? What use have astronomers made of the eclipses of Jupiter's satellites? At what distance from the sun, in what time, and at what rate does Saturn perform his annual revolution? What is the diameter of Saturn? What is the nature of the ring round Saturn? How many moons has Saturn? What is the figure of Saturn? What is the apparent cause of Saturn's being very much flattened at the poles? What are Dr. Herschel's measurements of the rings of Saturn?

CHAP. XXI.

ASTRONOMY · - continued.

THE FIVE NEW PLANETS.

FROM certain inequalities in the motions of Jupiter and Saturn, some astronomers had in

ferred that there existed beyond the orbit of Saturn, some planet by whose action those inequalities were produced.

This supposition was confirmed by the discovery which Dr. Herschel made of a new planet in 1781. In compliment to the king his patron, he named it the Georgium Sidus, though, on the Continent, it is better known by the name of Herschel, or Uranus.

This planet is distant from the sun, 1800,000,000 of miles, and performs its sidereal revolution. round the sun in eighty-three years, 150 days and 18 hours. Its diameter is 35,112 English miles. The Georgium Sidus, being at a vast distance from the sun, can scarcely be distinguished by the naked eye. When the sky is very serene, however, it appears like a fixed star, of the sixth magnitude, shining with a bluish white light, and a brilliancy between that of Venus and the Moon. Six satellites have been discovered also, by Herschel, revolving round this distant planet, supplying its deficiency of light received from the sun.

The planet Ceres was discovered by the astronomer Piazzi, at Palermo, in 1801. It is of a ruddy colour, and appears about the size of a star of the eighth magnitude. It seems to be enveloped by a thick atmosphere. Ceres performs her revolution round the sun in four years, seven months, and ten days, and her mean distance from that luminary is nearly 260,000,000 of English miles. According to the measurement of Dr. Herschel, the diameter of Ceres does

not exceed 160 miles, while the German astronomer, Schroeter, computes it to be 1624 miles.

The planet, named Pallas, was discovered by Dr. Olbers, at Bremen, in Lower Saxony, A.D. 1802. It is nearly of the same magnitude as Ceres, but of a less ruddy colour, is surrounded by a nebulous atmosphere of almost the same extent, and performs its annual revolution in about the same period, of four years, seven months, and ten days. It is distinguished, in a very remarkable manner, from Ceres, and all the other primary planets, by the immense inclination of its orbit, for it ascends above the plane of the Ecliptic, at an angle of about thirtyfive degrees; which is five times greater than the inclination of Mercury. The orbits of Ceres and Pallas intersect each other, a circumstance which does not take place in any other part of the solar system.

The planet, called Juno, was discovered by Harding, at the observatory of Lilienthal, near Bremen, in 1804. This planet is of a reddish colour, and free from the nebulosity which surrounds Pallas. Its diameter is less, and its distance greater, than those of the other three proximate planets. This planet performs its revolution round the sun in somewhat more than five years. Its mean distance from the sun is 275,000,000; its diameter, 1425 miles.

In 1807, Dr. Olbers discovered another planet, to which he gave the name of Vesta. It is about the fifth or sixth magnitude, and may be discerned by the unassisted eye, in a clear state of atmosphere. Its light is more intense, pure and

white, than that of the other three. The orbit of Vesta cuts the orbit of Pallas, but not in the same place where it cuts that of Ceres. Its revolution round the sun is performed in somewhat more than three years.

QUESTIONS.

When was the Georgium Sidus discovered, and by whom? What is it usually called on the Continent? At what distance is the Herschel from the sun, and in what space of time does it perform its revolution round the sun? What is its diameter? Is the Georgium Sidus distinguishable by the naked eye? Has the Herschel any moons? When and by whom was the planet Ceres discovered? At what distance from the sun, and in what time, does Ceres perform her revolution? What is the diameter of Ceres? When, and by whom, was the planet, called Pallas, discovered? What is the magnitude of that planet, and what is its appearance? For what is Pallas principally remarkable? When was Juno discovered, and by whom? What is its appearance? At what distance from the sun, and in what time, does Juno perform her revolution round that glorious luminary? When, and by whom, was the Vesta discovered? What is its appearance? In what time does Vesta accomplish her solar revolution?

CHAP. XXII.

ASTRONOMY― continued.

COMETS SYSTEMS.

COMETS are bodies which revolve round the sun, but in very eccentric orbits, and therefore appear in the heavens only occasionally. They exhibit no defined disc, but shine with a pale

and cloudy light; and are accompanied by tails or trains, turned from the sun. When viewed through glasses of high power, à comet resembles a mass of aqueous vapours encircling an opake nucleus, of different degrees of darkness in different comets; but, in some, no nucleus is discernible.

In its advance towards the sun, the faint cloudy light of the comet becomes more brilliant, and its luminous train gradually increases in length. When it comes to that part of its orbit which is nearest to the sun, the length of its tail reaches its utmost point, and its lustre sometimes equals that of Venus. As it departs from the sun, it loses its splendour gradually, till it resumes its nebulous appearance, and its train decreases. It continues diminishing till it reaches such a distance from the earth, as no longer to reflect the sun's light with strength sufficient to render it visible to human eyes.

Travelling unseen through the remoter parts of its orbit, the comet pursues its course far beyond the limits of our system. After the lapse of years, it is again seen returning to our system, and tracing a portion of the same orbit round the sun which it had formerly described.

During the dark gloomy night of barbarism and error, comets were regarded with terror, as the harbingers of calamity and ruin. Even so late as the beginning of the eighteenth century, they were considered by some to be the seats of woe and punishment, destined for the wicked, in which they would experience the extremes of heat and cold. By others, comets