78 LIGHT SCIENCE FOR LEISURE HOURS. 



interest connected with this explanation, the following 

 process may be employed. Let the reader draw a circle 

 ten and three-quarter inches in diameter to represent 

 the sun or moon as we see these orbs. At the centre 

 of this circle draw a small one, one-tenth of an inch in 

 diameter ; this will represent the earth as seen from 

 the sun. Three inches from this small circle set 

 another, a fortieth of an inch in diameter ; this will 

 represent the moon as seen from the sun when at her 

 greatest range of distance from the earth. Exactly on 

 the opposite side of the little circle representing the 

 earth, and three inches from that circle, set another 

 little picture of the moon ; this represents the moon as 

 seen from the sun when at her greatest range of dis- 

 tance from the earth on the other side. The observer 

 in the sun would see the moon pass backwards and 

 forwards from one position to the other in rather more 

 than four weeks. In thus moving backwards and forwards 

 the moon passes always close (in appearance) to the earth, 

 but sometimes closer than at others, and sometimes right 

 across or right behind the earth's face. The path, 

 in fact, opens out into an oval whose greatest width, 

 on our scale, is slightly more than five-tenths of an inch, 

 then closes up, then opens out to the same degree, only 

 tilted the other way, then closes up again, and so on 

 continually, while the earth all the time is circling 

 round the observer's standpoint once in a year, and the 

 moon round her path (thus varying in aspect) 1 once in 



1 Of course the path is not a real entity, and could not therefore 

 be seen, as supposed. It is convenient, however, to regard it as such. 



