t 203 ) 



èntirelv preliminarv character of niy result for the length of the 

 period, if I had not thought luy meaning sufficiently evident. At all 

 events I assuredly think that, in formulating my result, I have not 

 lost sight of the prudence necessary under these circumstances. Thus 

 I give, beside my result of 431.11 days, also the one which would 

 follow if the mean epoch found by H. G. v. D. S. Bakhctzex 

 "were combined with mine, viz. 430.36, whilst finally I observe that 

 for the last 35 years the length of the period cannot have differed 

 considerably from 431 days and that such a great variabilitij as 

 Chandler assumes, is now already contradicted by the observations. 

 So I believe I may state that the words of Dr. Chaxdler: „stre- 

 „nuously maintain that the mean period is more than 431 days, 

 „and that it is invariable" show but very inaccurately the stand- 

 point taken up by me ^). 



Let this suffice to answer Chandler's observations about the 

 treatment followed by me ; his remarks concerning the facts themselves 

 will be presently coosidered. 



3. Before discussing the results furnished by my later computations 

 on the length of the period, I will concisely state the results arrived 

 at by Chasdlek in 1S94 (Astr. Joura. X". 322) and those lately 

 deduced by him. His formula of 1S94 gave as Epochs of minimum 

 in the 14 -monthly motion : 



T = 2402327>» + 428'».6 E -\- 55-^ sin W | 



in which, with a sufficient approximation ' (1) 



W — (/— 1865.25) . 5°.48 = EX 6°.43 | 



From this there results for the length of the period, osculating 

 for the epoch E: 



P — 428>i.G -L 61.2 COS {E X ö°.43) (2) 



So the length of the period may vary from 434'*.8 to 422'^.4 and 

 the cycle of this change embraces 56 periods or 66 years. The 

 maximumlength would have been reache<l in 1865, the minimum- 

 length would take place in the present year 1893. 



In his last paper Chandler starts with this formula and tests it 

 by the observations of 1890 to 1897. He does not use the ^ and y of 

 Albrecht, but values derived by himself, which however agree with 



') Neither are his words accurate, whsre they coacani H. G. v. d. S. BiKfioifZEN. 

 See a. o. Astr. Xacbr. N". 32'ó, page lö3 at the top. 



