ROTUNLHTY Ol- THE EAKTH. lO 



light and shade, ascends the heavens, reaches the highest point 

 and declines in the west. Star after star sinks beneath the 

 western hills, and new ones rise in the east. Twelve hours pass 

 away, when again the sun, rising with undiminished lustre, calls 

 the busy world once more into bustle and activity. 



The phenomena thus presented, convince us that there is no 

 such thing as rest, for the whole heavens seem revolving around 

 us, and the first step towards an accurate knowledge of our earth 

 is, that either we, or the heavenly bodies, are in ceaseless and 

 regular motion. 



Suppose that before us the waters of some vast lake or ocean 

 are spread out ; far as the eye can reach the're seems to bo a place 

 where the sky is resting upon the water, called the horizon from 

 a Greek word meaning "to see." As we stand, perhaps won- 

 dering how far from us this horizon is, a vessel sails out the harbor 

 and moves steadily from us. Now our first idea is that we are 

 looking out upon a vast plain, and consequently .we expect to see 

 the vessel as it moves away, become fainter and fakiter, until at 

 I ast the straining eye will fail to catch the minute image. This 

 appearance is shown in the engraving below. 



Instead of this, however, a new and unexpected phenomenon 

 greets the eye. The vessel sails away, and soon arrives at the 

 horizon, and then slowly sinks from view. First the hull disap- 



