434 ASTRONOMY. 



In consequence of the earth's being a globe, 

 people standing upon opposite sides of it must have 

 their feet towards each other. When in this 

 situation, they are called antipodes to each other. 

 Hence it appears that there is no real up or down; 

 for what is up to one country is down to another. 

 It must seem strange to those who are ignorant of 

 the shape of the earth, to suppose that if we could 

 bore a hole downwards, deep enough, we should 

 come to the other side of the world, where we 

 should find a surface and sky like our own; 

 yet if we reflect a moment we shall perceive that 

 this is perfectly true. As we are preserved in 

 our situations by the power of attraction, which 

 draws us towards the centre of the earth, we 

 call that direction down, which tends to the 

 centre. 



We mentioned before, that the earth has two 

 motions; the one a diurnal motion, round its own 

 axis; the other an annual motion, round the sun. 

 It is the former which causes light and darkness, 

 day and night; for when one side of the earth is 

 turned towards the sun, it receives his rays, and 

 is illuminated, causing day ; on the contrary, when 

 one side of the earth is turned from the sun, we 

 are in darkness, and then we have night. We 

 see, therefore, by how much more simple means 

 this change is effected, than they imagined, who 

 supposed that the earth was fixed, and that the 

 immense globe of the sun was whirled round the 

 earth with the amazing velocity that would be 

 necessary. 



Twilight is owing to the refraction of the rays of 

 light by our atmosphere, through which they pass, 

 and which, by bending them, occasions some to 



