OBSERVATIONS WITH THE ZENITH TELESCOPE. 



323 



zenith distance was as great as twenty revolutions. In such cases threads II and IV were 

 used to avoid the large number of turns of the screw. 



The distance between II and IV was therefore required with accuracy and was 

 determined at frequent intervals. Below will be found the amount to be added to the 

 micrometer correction required on account of the amount by which II-IV differed from 

 twenty revolutions. The progressive diminution is evidently due mainly to the increased 

 value of B from wearing : 



1892 October 10 



// 

 1 1.54 





1893 



February 24 



ii 

 + 0.83 



October 14-November 17 



1.25 







25 



| 0.82 



November 20 



1.20 







February 26-,lu1y 21 



+ 0.81 



22 



+ 1.16 







July 23 



+ 0.77 



26 



-1 1.11 







27-August 10 



+ 0.74 



December 1-Decem.ber 11 



| 1.05 







September 8-September 22 



-|- 0.55 



2 



| 1.01 







83 



-| - 0.48 



12 



+ 0.97 







27-October 24 



1-0.42 



15 



| 0.94 







October 25 



+ 0.30 



17 



+ 0.90 







28 



+ 0.31 



December 18-February 15 



|- 0.80 







October 29-November 10 



1 0.25 



L898 February 16 



+ 0.85 







November 26 



+ 0.16 



20 



+ 0.84 







" 28-Deeember 25 



+ 0.00 





The 



Star 



hist. 



' . 





The list of stars found in the following pages shows the values of the coordinates 

 for 1892, '1)3 actually employed in the latitude reduction. The Right Ascensions differ 

 slightly from the definitive values, but this is of no importance for present purposes. 

 The last column, headed " correction for curvature," is the only one which appears to 

 call for explanation. This is the sum of the values of the quantity 



J -(15 T) a sin 1" tan <5 



Computed for each star of the pair, T being the interval from the time of bisection to the 

 time of passing the meridian. 



The reduction to apparent place was made by the formula, 



J (,J +,)'') = i (6 + ,?'„) | \ di' + //,') r + I (a' + a/) A + j (fi> + ?+) B + j (c' + c,') O + I (d> + <V) D 



A, />, (7 and J) being taken from the American Ephemeris. 



