18 



INTKODUCTION 



the stars change their places. The sun itself is ohserved to turn round. If we mvestigate 

 still further, we slmll discover that these brilliant orbs, which occupy the heavens, are all of 

 them worlds, some of them larger and some smaller, all moving in their appointed courses, and 

 all fulfilling the will of the Almighty Architect who made them. 



The study of the heavenly bodies is called astronomy : geography, strictly speaking, is a 

 description of the earth. However interesting and wonderful the subject of astronomy may 

 be, we can only attend to it here, so far as may be necessary to complete our view of the 

 globe we inhabit. 



2. Fixed Stars. Constellations. The stars nearest to our earth are grouped into signs or 

 constellations, for the convenience of description ; but the more distant appear to the eye as 

 nebulous patches or streaks of diluted light, which optical instruments have enabled us to 

 resolve partially into clusters of stars, and these analogy teaches us to regard as myriads of 

 suns ; while imagination, ranging through illimitable space, pictures still more remote orbs, 

 whose light has for ages travelled the vast profound, without yet reaching the abodes of man. 

 The great mass of these stars appear to us to remain in the same relative situation, and have 

 therefore been called Fixed Stars., although it is probable that they are all in a state of motion. 

 Their number seems to be beyond calculation, their distance from the earth is too great to be 

 measured by hun.an skill ; but mathematical considerations show us, that it cannot be so small 

 as nineteen trillions of miles ; how much larger it may be we know not. 



3. Solar System. But the celestial bodies with which we are most familiarly acquainted, 

 are those which are called planets or wanderers, and which revolve around the sun as their 

 common centre of gravity. These bodies, of which the terraqueous globe is one, together 

 with several secondary planets which revolve around the larger, an unknown number of 

 comets, and the Sun itself, the great central mass, form what is called the Solar System. 



(1.) Primary Planets. Those planets which revolve around the sun are called primary 

 planets, and the number at present known is ten, beside our Earth, but it is not at all improb- 

 able that there may be others yet undiscovered. Four of them are reniarkably large and 

 brilliant. Venus, iMars, Jupiter, and Saturn ; another, Mercury, is also visible to the naked 

 eye as a large star, but, on account of its nearness to the sun, is seldom conspicuous ;a sixth, 

 Uranus or Herschel, is barely discernible without a telescope ; and four others, Ceres, Pallas, 

 Vesta, and Juno, are not visible to the naked eye. Five of these planets. Mercury, Venus, 

 Mars, Jupiter, and Saturn, have been known and named from the earliest ages of history ; 

 Uranus or Herschel was discovered by Herschel in 1781, and the other four have been dis- 

 covered still more recently. Saturn is distinguished from the other ])lanets by its being sur- 

 rounded by two luminous rings concentric with itself, which are visible only by means of a 

 telescope. 



(2.) Satellites. The smaller bodies, which revolve round 

 several of the primary planets, and probably serve as moons 

 to their inhabitants, are called secondary planets or satellites. 

 The number of satellites certainly known is fourteen, four 

 more are suspected, and it is not impossible that the number 

 may even be larger ; of these, one, the moon, belongs to the 

 earth, four to Jupiter, seven to Saturn, and certainly two, 

 probably five or six, to Uranus. 



(3.) Comets. A third class of bodies belonging to the 

 solar system, are the comets., with the nature of which we have 

 but sHght acquaintance. Their actual number is unknown, 

 but is supposed to amount to some thousands. They gener- 

 ally consist of a large and splendid, but ill-defined nebulous 

 mass of light, called the head., which is usually much brighter 

 towards the centre, and ofl^ers the appearance of a vivid 

 nucleus., like a star or planet. From the head, and in a 

 direction opposite to that in which the sun is situated from the 

 comet, appear to diverge two streams of light, which grow- 

 broader and more diffused at a distance from the head, and 

 which sometimes unite at a little distance behind it, and some- 

 times continue distinct for a great part of their course ; this 

 s called the tail Some comets, however, have no tail, and some have as many as five or 



Saturn with its Satellites. 



