290 THE BOTTOM OF THE SEA. 



stars are seen in the same places as if the centre of 

 the earth were a fixed position — that is to say, as if 

 it always pointed to the same spot in the heavens. 

 This constant parallelism of the earth's axis is, how- 

 ever, only apparent. In reality, it shifts to the 

 extent (taking the extreme limit) of 4°, its revolution 

 describing a cone in about 20,000 years. 



If the stars are thus shifted from their apparently 

 fixed position, their relative situation is at least con- 

 stant, you will say ? Careful observation, extended 

 over many years, has shown the contrary. The 

 whole solar system is moving, as if it were one com- 

 pact and independent organisation, through space. 

 Astronomers have demonstrated that it is approaching 

 the constellation Hercules, but it would require ages 

 of observation to detect any variation in the relative 

 positions of the fixed stars. Such observation would 

 demonstrate by an extraordinary effect of perspective, 

 which it is no part of our present business to ex- 

 plain, that their distance from Hercules is in- 

 creasing. 



Every day the sun rises above the horizon, and 

 Bets at the opposite extremity of the heavens ; so the 

 lieat of the day succeeds constantly the cold of the 

 night. Year after year the ice is melted by the 

 soft breath of the spring ; year after year summer 

 ripens the fruits of the earth. Year after year 



