264 



TRANSIT OP VENDS, 1874. EGYPT. 



The Pivot Correction was determined by repeated reversals of the instru- 

 ment as follows : 



1874, June 1 8, o'65i divisions 



23, 'o38? 



24, -879 

 26, '990 



29. '976 ,, 



30, ' goo ,, 

 July i, -759 







5) 



A positive level-error was 

 greater with the Micro- 

 meter East than with the 

 Micrometer West. 



The pivot correction applied to the level-error determined by spirit-level is 

 0"'94 Micrometer East and 4- 0"'94 Micrometer West. 



The Zero of Gollimation has been obtained from observations of circumpolar 

 stars with reversed positions of the transit axis (Table XIV.). 



The Error of Azimuth (Table XV.) has been found in the usual way, by 

 combining the observed transits of two stars, one of which was near the pole. 



The transits of stars (Table XVI.) have been reduced as described in 

 Part I., page 15. The table contains only the transits observed in connection 

 with important operations, such as longitude signals and the actual transit of 

 Venus. When a transit was imperfect, or less than five bisections of a polar 

 star with the micrometer were obtained, the number of wires, or bisections, 

 observed is indicated by a numeral attached to the star's name thus : " e Eridani 

 (4)." For the polar stars the mean micrometer-reading corresponding to the 

 mean observed clock-time is also given with the star's name, and the micro- 

 meter-setting for Clock Stars is given at the foot of the page. 



For the diurnal aberration a constant ( 0"'27) has been embodied in the 

 correction for Gollimation ; the tabular Right Ascensions in Column 7 are 

 therefore not affected by it. "When a circumpolar star has been observed 

 with both positions of the instrument, each observation is separately reduced, 

 and the clock-slow for such observations is deduced, to exhibit the accuracy or 

 otherwise of the instrumental corrections. 



The adopted error of the transit clock (Table XVII.) is the simple mean of all 

 the errors obtained on the day (omitting of course those obtained from polar 

 stars), and corresponds to the mean of the observed sidereal time in Column 3. 

 The adopted losing rate in Column G is the mean of the observed loss in the 

 24 hours preceding and following, and also corresponds to the mean of the 

 times. When the interval of time for which clock rate has to be allowed for any 

 species of observation exceeds six hours, the " loss in 24 hours " in Column 5 



