Forces on the Motion of the Moon. 539 



motion of the moon's center of mass. This is due to the near 

 coincidence with the period of revolution of the moon's node. 

 But since the amplitude of the inequality in the moon's motion 

 is directly proportional to the ellipticity, the amplitude of the 

 free libration must be proportionally increased so that it would 

 have to be of the order of 800 ". It seems doubtful that such 

 a large term should have escaped detection. 



The results of these various computations are therefore not, 

 on the whole, favorable to the hypothesis that a librational 

 term causes the long-period inequality in the moon's motion. 

 But the magnitudes of the forces which have been considered 

 are so small that a more careful examination into the question 

 of the whole effect of a magnetic attraction on the motion of 

 the moon about its center of mass seems to be a desideratum, 

 in view of the discordance between the theoretical and the 

 observed ellipticities. This is not the object in view here, but 

 the effects are not confined to any one class of observations and 

 it may be possible to obtain evidence from various sources by 

 which the question can be settled. 



Yale University, April 7, 1910. 



