URANUS. Since the time of the discovery of this planet by the illustrious Her- 

 tehel, little has been added to our knowledge of him. He is certainly attended by 

 t least four satellites, possibly more, and their revolutions are performed iti a 

 direction contrary to the general movements of the planetary system, from west to 

 east; while the inclination of their paths to the ecliptic,- one oi "which forms an 

 angle of only 11 deg. 2 min. with a perpendicular to it-s plane, is another deviation 

 from what would seem to be the existing arrangement with all the other planets, 

 except Neptune. 



NEPTUNE. This, the most distant of the known planets in the solar system, was 

 discovered by Messrs. Adams and Le Verrier, in 1846. He revolves at tue vast 

 distance of 2,862 millions of miles from the sun, and occupies 164 years in per- 

 forming his vast circuit round that luminary, although he travels at the rate of 

 12,500 miles an hour. The discovery of a satellite to this remote planet is due to 

 Mr. Lassel, of Liverpool ; and it is found to travel in the same retrograde order as the 

 satellites of Uranus. 



COMETS 



Besides the planets already described, there is an unknown, number of other 

 bodies, called COMETS, which revolve round the sun in very elliptical orbits. Their 

 period of revolution is so long that very little is known respecting them. They 

 are only seen by us when they are in that part ot their orbits which is nearest the 

 sun, and then they move with such vast rapidity that they soon become again in- 

 visible to us. They are not all alike in appearance ; some appear like a faint 

 vapour, while others have a solid part in the middle. When they approach the sun, 

 they have a tail of luminous matter, which is sometimes of astonishing length, 

 and always directed from the sun. 



The conjectures of many eminent astronomers respecting the nature and causes 

 of the tails of comets, show that they are not yet understood. Some have thought 

 that it was the atmosphere of the comet driven behind it by the force of the solar 

 rays. Sir Isaac Newton considered that the tail is a thin vapour raised by the heat 

 of the sun from the comet. Probably neither of these conjectures is right ; and 

 the nature, uses, and laws of comets are left for future discovery. 



THE EARTH, 



Having described the solar system, and the planets which compose it, with the 

 exception of the Earth, we have reserved the latter, on account of its importance 

 to us rendering it desirable to describe it in connection with the celestial phenomena 

 with which it is associated. 



The diameter of the Earth is 7,912 miles; its circumference at the equator 

 24,900 miles; and its mean distance from the sun 95,000,000 miles. The Earth 

 performs its revolution round the sun in 365 days 6 hours, forming our year ; and 

 turns upon its axis in about 24 hours, producing the phenomena of day and nigh*. 



The ancients considered that the Earth was a large flat plain, surrounded by 

 water ; but what there was beyond this mass of land and water, or what there was 

 below it, or how the Earth was supported, were problems they were unable to solve. 

 At length men became more enquiring, and it was discovered that the earth is 

 globular, or round ; but it has been only within the last th-ree hundred years that 

 the true figure of the earth has been ascertained. 



THE ATMOSPHERE. 



The earth is surrounded on all sides by the atmosphere, which extends to the 

 height of about forty-five miles, decreasing in density in proportion to the altitude. 

 Among its important properties, it possesses that of REFRACTION ; that is, a ray 

 of light from any celestial object, in passing through the atmosphere becomes re- 

 fracted, or bent out of a straight line, and is deflected towards the earth. This 

 occurs to the greatest extent when the celestial object is near the horizon ; and, as 

 a consequence, it appears to us higher than it really is, because we see all things in 

 the direction in which their rays last approach the eye. It is owing to this that 

 the sun is seen some minutes before it rises above the horizon and after it has 

 sunk below it. 



DAY AND NIGHT 



In order that this phenomena may be clearly understood, it must be borne in 

 mind, first, that the earth is round ; secondly, that it receives its light from the 

 sun ; thirdly, that a globe cannot be illuminatejd on both sides at the same time by 

 one luminary ; fourthly, that if both sides are to enjoy the light, it must be in suc- 

 cession ; thus, while one sidi is enlightened, the other side must be in darkness 



