( 2(16 ) 



We see that a 428 days' period satisfies the original observations 

 almost as well as a 431 days' period. 



On the other hand a 423 days'period leaves considerably greater 

 errors, which are but slightly diminished by deducing anew also the 

 yearly motion, as is shown by the numbers given in the last place. 



So our result is, that the observations from 1890 — 97 prove in 

 themselves a 423 days' period to be improbable; but much farther 

 than that we cannot go. 



5. In the second place I had recourse again to the older series 

 of observations, but, before discussing this investigation, I will state 

 that, now again, it lays no claim to completeness. 1 have only again 

 combined the results of observations treated already by others, with 

 each other and with my results for 1890 — 1897 and from these I 

 have drawn such conclusions as seemed most probable to me. The 

 observations of Pulkowa 1863 — 1875 only make an exception, as 

 for these I made a computation myself founded on the results arrived 

 at by IVANOFF in two important papers. ') 



First came the question how far we may go back in the employ- 

 ment of older observations and this again depends upon that other 

 question, whether we assume in the 14raonthly motion a lasting 

 continuity, or whether we do not exclude the possibility that more 

 or less sudden changes may take place. 



As is already remarked. Chandler includes amongst the conclusions 

 formulated in his last paper, also this one, „that a change per saltum 

 „between 1830 and 1860 is incompatible witli the facts". To me 

 on the contrary it seems that there is every reason to assume the 

 possibility of such a change between 1840 and 1860. 



This statement is based in the first place on the values for the 

 amplitudes as they have been found before 1860 and after that 



') A. IVANOFF, Variations de la latitude de Poulkovo dédiiites des observations 

 1863—75. (Mc'lanaes math, at astr. T. VII.) St. Pétersbourg 1S91-. 



A. Iv.vNoi', Eeelierolips dc'tinitives sur les variations de la. latitude de Ponlkovo 

 (Bull. Acad. IV-tersb. Serie V. T. It). St. Pétevsbour,; Isyö. 



