WEIGHING THE WORLDS 



out in space, it would seem to shift its position back 

 and forth, always however maintaining the same re- 

 lation to the moon. And, contrawise, a stationary 

 object in space as viewed from the earth would seem 

 to shift its position back and forth in half-monthly 

 periods. The amount of this shift would be so small 

 in the case of bodies at stellar distances as to be quite 

 inappreciable; but on the other hand it would affect 

 the seeming position of a body as near as the sun 

 quite materially. 



In point of fact, such an oscillation in the seem- 

 ing position of the sun is observed actually to occur. 

 As the earth rotates twenty-eight times on its axis 

 during each monthly period of revolution, the sun 

 is brought as many times to the meridian during 

 each such period; and it is observed that when the 

 moon is "new" and aga'in when it is "full" at which 

 times, it will be obvious, the orbital centre of earth 

 and moon falls in direct line with the sun and the 

 moon the sun comes to meridian exactly at the pre- 

 dicted time. But when the moon is in the first quar- 

 ter the line connecting the earth and moon being 

 at right angles to the earth and the sun the sun's 

 seeming position will be shifted in such wise that it 

 comes to the meridian a little later than the predicted 

 time ; and again when the moon is in the last quarter 

 a seeming shift in the opposite direction brings the 

 sun to the meridian a little before the predicted time. 

 Of course at intermediate periods there is a transi- 

 tional shift in one direction or the other day by day. 



The measurement of the maximum shift in the 

 sun's seeming position determines thQ actual shift in 



