Solar System. 51 



r2290 miles every hour ; and turns round 

 her axis exactly in the time that she goes 

 round the earth, which is the reason of 

 her keeping always the same side towards 

 us, and that her day and night taken to- 

 gether is as long as our lunar month. 



The moon is an opaque globe like the 

 earth, and shines only by reflecting the 

 light of the Sun ; therefore whilst that 

 half of her which is towards the sun is 

 enlightened, the other half must be dark 

 and invisible. Hence she is incessantly 

 varying her appearance ; sometimes she 

 looks full upon us, and her visage is all 

 lustre ; sometimes she shews only half 

 her enlightened face, soon she appears as 

 a radiant crescent, in a little time all her 

 brightness vanishes, and she becomes a 

 beamless orb. The full moon, or oppo- 

 sition, is that state in which her whole 

 disk is enlightened, and we see it all 

 bright, and of a circular figure. The 

 new moon is when she is in conjunction 

 with the sun ; in this state, the whole 

 surface turned towards us is dark, and is 

 therefore invisible to us. The first quar- 

 ter of the moon she appears in the form 

 of a semicircle, whose circumference is 



