52 . Solar System. 



turned towards the west. At the last 

 quarter she appears again under the form 

 of a semicircle, but with the circumfer- 

 ence turned towards the east. These 

 phases may be illustrated in a very plea- 

 sing manner, by exposing an ivory ball 

 to the sun, in a variety of positions, by 

 which it may present a greater or small- 

 *er part of its illuminated surface to the 

 observer. If it be held nearly in opposi- 

 tion, so that the eye of the observer be 

 almost immediately between it and the 

 sun, the greatest part of th^; enlightened 

 side will be seen ; but if it be moved in a 

 circular orbit, towards the sun, the visi- 

 ble enlightened pari will gradually de- 

 crease, and at last disappear, when the 

 ball is held directly towards the sun. Or 

 to apply the experiment more immedi^ 

 ately to our purpose ; if the ball, at any 

 time when the sun and moon are both 

 visible, be held directly between the eye 

 of the observer and the moon, that part 

 of the ball on which the sun shines, will 

 appear exactly of the same figure as the 

 moon itself. 



The moon has scarce any difference of 

 seasons ; her axis being almost perpenv 



