OBSERVATIONS WITH THE ZENITH TELESCOPE. 



309 



Each pair, with two exceptions, was observed both evening and morning. The 

 number of evening observations was 842, of morning 637. 



The reduction to apparent declination was carried through twice for each date of 

 observation, once by each of the standard formula;, viz. : 



and 



6 = 6 + Til' + An' -I- Bb> + Co' + I)d> 



6 = c? -\- r/1.1 -\ g cos ( O ■]-- «„) -|- h cos (II -\- a ) sin S + ''< COS < v „ 



A, B, C, J), h, If, (j, G and i were taken from the American Ephemeris. 



The Latitude Observations. 



In planning this series of Latitude determinations the effort was made to observe 

 each pair not less than five times, both evening and morning. Practically a few pairs 

 were observed as many as twelve times, and in a few cases the number fell short of five. 

 The evening observations were naturally more numerous than the morning. The usual 

 method was to begin work soon after sundown and to observe from one to three or four 

 hours, then to begin in the morning two hours or more before daylight and to stop 

 only when sunrise ended the operation. Some of the brighter stars were observed with 

 the sun above the horizon. 



No attention was given to arranging the pairs in groups to facilitate adjustment. 

 Under these circumstances, in connection with the fact that considerable care has been 

 given to the reduction of the declinations, it is perhaps doubtful whether much will be 

 gained by such an adjustment. The attempt has been made, however, to improve the 

 results in this manner. 



For this purpose the series has been divided into ten groups as follows : 



h m h m 



(J roup 



I w 



gilt Ascension 



22 



20 - 



- 



27 



11 pairs 



II 









B8 ■ 



- 3 



01 



10 



III 





3 



04 - 



- 5 



34 



11 



IV. 





5 



41 - 



- 7 



24 



10 



V 





7 



29 - 



- 9 



35 



12 



VI 





9 



47 ■ 



- 12 



30 



11 " 



VII 





12 



57 - 



- 15 



00 



11 



VIII 





15 



17 - 



17 



24 



12 



IX 





17 



30 - 



- 19 



49 



11 



X 





19 



50 - 



- 22 



10 



12 



Reduction to Mean of Groups. 



When every pair of a, given group has been observed on any night, the mean of the 

 resulting latitudes will be based upon ihv, mean value of (be declinations of all stars of 



A. I", s. — VOE. XX. NN. 



