THE MOON IN MASQUERADE 113 



liminary. The gravitational effect of the sun on the 

 inoon, after all allowances as to distances are made, is 

 a little more than twice that of the earth. Hence it may 

 be asked why the moon does not settle with its center 

 of gravity turned sunward instead of earthward; in 

 which case it would show every side of itself to us, bnt 

 keep one side only perpetually directed to the snn. The 

 answer to this is not difficult. The test is not one of 

 degree of power alone, but of differentiation of power. 

 For the sun being some 400 times more distant than the 

 earth, the angle formed by two lines drawn from its 

 center to the two points marking respectively the cen- 

 ter of figure and the center of gravity of the moon (for 

 the two are by no means identical) will be only 1/400 

 as great as a similar angle formed from the earth's 

 center to the same points. Hence the sun cannot bring 

 its greater strength so well to bear. It is a question 

 of purchase, or twist. Now, as the moon progresses in 

 her orbit she keeps shifting her angular position rela- 

 tive to these rival attractions of sun and earth, and this 

 it is that produces the libration in question. Thus 

 when she is at new and full, the sun and earth act along 

 the same straight line; but when she is at the quarters, 

 their attractions conflict most, and the moon swings 

 east or west accordingly. 



In a former chapter I explained how the earth and 

 moon together are kept revolving around the sun by the 

 action of the Prime Resultant, so that, including it, 

 we have three rival forces continually pulling at the 

 moon, all together being capable of accounting from 

 instant to instant for all its varying movements. If, 

 now, to these were added an inherent, arbitrary rota- 

 tion as predicated by current theory, it is plain that the 

 moon's safety would be imperilled. Like a weather vane 

 it has to be, and it is, free to respond automatically to 

 the eddying currents continually playing upon it, only 



