33 



— = + 2".28 ; -^ = — 2".22. 

 dt dt 



Perturbations caused by the second ellipsoid. 



I find: 



^— - = - 2 {a' — c') E^sin <p sir, ,/; ™-— = 2{t/-' — c') E^ cos sm,/ ; 

 d.voz ' oyoz \ 



-^ = -2E,-^a'^-c^)E, 



from vvhicli Ibllows: 

 R 1 a'' 



A- 2{a^ — c^) a ^ ^ E^sin J siv i cos {\X— </») | . 



Although the term a"^ — c^ is not small, yet it is allowed to omil 

 the periodic term. 



Ï get E^ = 0.684, E^ = 2.445 from which follows taking as unit 

 of time the century : 



dco ,, dsl 



— = — 0".16 ; — = -0"28. 

 dt dt 



Tims both ellipsoids together give : 



— = -I- 2".12 ; ^:=J. 2"5i'; 

 dt ^ dt ^ 



l)oth insejisible amounts. 



Astronomy. — ''Remarks on Mr. Woltjer'.s' paper concernimi 

 Skeliger'.s' hypothesis." By Prof. W. de Sitter. 



(^Communicated in the meeting of April 24, 1914). 



Seeligek's explanation of Newcomb's anomalies in the secular 

 motions of the four inner planets consists of three parts, viz : 



a. The attraction of an ellipsoid entirely within the orbit of Mercury 

 The light reflected by this ellipsoid is, on account of the neighboui-- 

 hood of the sun, invisible to us. ' 



b. The attraction of an ellipsoid which incloses the earth's orbit. 

 The light reflected l)y this ellipsoid appears to us as the zodiacal light. 



c. A rotation of the empirical system of co-ordinates with reference 



3 

 Proceedings Royal Acad. Amsterdam. Vol. XVII 



