80 LIGHT SCIENCE FOR LEISURE HOURS. 



the moon is thrown into shadow, or eclipsed. So that 

 when the moon's path, as seen from the sun, is most open 

 forming then a long oval there can be no eclipses 

 either of the sun or moon. But when this path has in 

 appearance closed up to a line, or nearly to a line, the 

 moon can no longer pass by the earth (as viewed from 

 the sun) without actually crossing the earth's disc or pass- 

 ing actually behind that disc. So long as this state of 

 things lasts there must be an eclipse whenever the moon's 

 backward and forward motion carries her past the earth. 

 We have seen that the moon's path had this aspect, or 

 is closed up into a straight line, as seen from the sun, 

 at intervals of about five months and three weeks. For 

 rather more than a month the path is sufficiently 

 closed for eclipses to occur. I have suggested for 

 these occasions the title of * eclipse months.' To show 

 how they succeed each other, take the following illus- 

 trative instance : Let January in any year be an 

 eclipse month, the middle of January being the time 

 when the moon's path appears closed up into a line as 

 seen from the sun. Then five months and three weeks 

 later, or about July 6, the path is again closed up into 

 a line as seen from the sun; and a period of rather 

 more than a month, having this date for its middle 

 or from about June 22 to about July 23 is again an 

 ' eclipse month.' Passing on from July 6, we reach in 

 five months and three weeks the date December 27, 

 which is the middle of the next ' eclipse month.' And 

 so on continually. 



Other matters connected with the recurrence and 



