494 



SCIENTIFIC RECREATIONS. 



and silica. The theory concerning falling stars has been already 

 mentioned. 



We have thus far taken a brief general view of the solar system, with 

 a few of the phenomena of the heavens. Our next step will be to consider 

 the sun, the planets, and the asteroids, according to the order of magnitude. 

 The asteroids we cannot consider separately, but the sun, moon, earth, and 

 the principal planets will yield us much interesting information as we 



Fig. 541. The heavens as seen from Saturn. 



examine them more closely. We shall then, as far as possible, look into 

 the domain of the fixed stars, constellations, and the nebulae, comment- 

 ing, as we proceed, upon the varied celestial and terrestrial phenomena 

 connected with the movements of the heavenly bodies. As is due to the 

 great centre of our system, we will commence with the SUN. But before 

 proceeding to do so, we must say a few words about the motion of the 

 heavenly bodies that is, the apparent motion of the rising and setting of 

 the sun and stars. 



The attentive observation of the starry heavens, even during a single 

 night, will convince us that all the visible stars describe circles which are the 

 smaller, the nearer the stars are to a certain point 

 of the heavens, P (fig. 542). In close proximity to 

 this point there is a tolerably bright star, called 

 the Pole Star, which has scarcely any motion, but 

 appears to the eye as always occupying the same 

 position. Hence a line, PP 7 , drawn from this star, 

 through the centre of the earth, c, represents the 

 axis around which all the heavenly bodies perform 

 their apparent motions. The part of the celestial 

 axis, P P' passing through the earth, is the earth's 



Fig. 542. Celestial axis. 



axis ; the north pole, of which p is on the same 



side as the pole star, and the south pole, p', is on the opposite side. 



We have, therefore, by the aid of the stars, determined the position of 



