Eclipses. 25 



year than in the preceding. From the time, 

 therefore, when the ascending node passes by 

 the sun, as seen from the earth, there will be 

 only 178 days before the descending node passes 

 by him. If, then, at any time of the year we 

 have eclipses about either of the nodes, we may 

 expect in about 1 73 days after to have eclipses 

 about the other node *. 



The nodes shift through all the signs and 

 degrees of the ecliptic in eighteen years and 225 

 days ; and in this time there would always be a 

 regular return of eclipses, if any complete num- 

 ber of lunations were finished without a fraction. 

 But this never Happens ; for if both the sun and 

 moon should set out together from a line of 

 conjunction with either of the nodes, in any 

 point of the ecliptic, the sun would go through 

 eighteen annual revolutions, and 222 degrees 

 over, and the moon through 230 lunations and 

 85 degrees of the 231st, by the time the nodes 

 came round to the same point of the ecliptic 

 again ; and therefore the sun would then be 138 

 degrees from the node, and the moon 85 degrees 

 from the sun f . 



After the sun, moon, and nodes, however, 

 have been once in a line of conjunction, they 

 will return nearly to the same state again in 223 

 mean lunations, or about eighteen years and ten 

 days, so that the same node which was in con- 



* Bonnycastle's Astronomy, lett. xxii. f Ibid. 

 TOL. II. c 



