30 Art. 3— K. Sotome 



zero at the equator, towards north and south latitudes symmetri- 

 cally. To ascertain Avhether this is actuall}^ the case or not, 

 observations at the equatorial zone are very desirable. 



The numerical results so far obtained I do not intend to regard 

 as definitive. But they may serve as a clue for the yet unsolved 

 problems, or an indication of the direction in which we must pro- 

 ceed in order to account for them. 



Now, as my argument has been advanced from two causes, viz. 



1. some regular movements of the zenith telescope; 



2. a defect of the spirit level, 



I may also state with diffidence the results to which my considera- 

 tions have led me, as follows: — 



If we assume a regular change of inclination of the zenith 

 telescope, varying with the seasons and the hour of the day, 

 the three phenomena, that is, z term, closing sum, and the 

 regular shift of the spirit level, can all become explicable to- 

 gether. Therein the defect of the level makes the error enter 

 into the latitude value and gives rise to the z term and closing 

 sum. 

 My idea, therefore, leads to the conclusion that these enigmatic 

 subjects in the latitude problems would disappear, if the level were 

 really a perfect instrument, or if we were to use another and an 

 ideal means instead of this insufficient instrument. 



The photographic observations made with the Cookson floating 

 zenith telescope at the Greenwich Observatory by Mr. Jones' are 

 very -important in regard to the present problem. The latitude 

 variation obtained from this series was compared with the results of 

 the International Latitude Service. Herein the agreements was 

 particularly improved, when the z term was subtracted from the 

 latter series. As to the aberration constant, the value 



20. "467 ± 0."UOG 



was obtained. In other words, this novel series of observations was 

 practically free from the z term and closing sum. Arguing from 



1) Monthly Notices of the E.A.S., Vol. LXXV, No. 7. 



