212 FKOM NEBULA TO NEBULA 



by Dr. Chandler's analysis. The 430-days term, how- 

 ever, demands elucidation: 



Were the sun and moon always in alignment with the 

 earth, and did they not move from their places, the si- 

 dereal day would be the same as the solar day and the 

 " lunar day' 7 (if we may permit ourselves this last ex- 

 pression for the sake of simplicity). In that case, there 

 would be no fluctuation of latitude at all. But the moon 

 is not stationary; she steadily gains over the imaginary 

 position we have just pictured her in, a position, how- 

 ever, which is monthly realized when she is said to be 

 new. Now, the time elapsing between new moon and 

 new moon is known as the synodical month, and its 

 length is 29.53059 days, whereas the sidereal month is 

 only 27.32166 days, consequently the latter in one year 

 gains on the first 2.20893 times as many days as 27.32166 

 days is contained times in 365 J4 days. Performing the 

 operations, we obtain 29.5 days, which, because the 

 moon's torsional effect is 2.25 times as great as the sun's, 

 must now be multiplied accordingly, yielding 66.4 days. 

 Adding this to the annual period, we have 431.6 days, 

 which is a very close approximation to Dr. Chandler's 

 second term, considering the many uncertainties and dif- 

 ficulties involved. 



A very interesting, not to say significant, coincidence 

 brought out by this avenue of investigation deserves to 

 be mentioned. If we average Dr. Chandler 's four frac- 

 tions (125-1000 sec.) and the two periods (398) days, and 

 multiply them together this on my hypothesis that the 

 variation is of diurnal causation we obtain 49". 75, a 

 quantity startlingly near the 50" .2 arc annually added 

 to the precessional circle! 



