408 TRANSIT OF VENUS, 1874. KERQUELEN ISLAND. OBSERVATORY BAY. 



that the correction to the level-error with the micrometer west was 0" P 80, 

 and this value has been applied throughout. 



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

 combining the observed transits of two stars of suitable declinations cor- 

 rected for level and collimation. Occasionally, the observations of the north 

 mark have been used to determine the azimuth-error ; but such was the 

 instability of the instrumental mounting, that it is never safe to deduce the 

 clock-error, unless a circumpolar star was observed at the same time as 

 the clock stars. For this reason several transits of the Moon cannot be 

 utilised. No stars were observed near the zenith; the rate of the clock, 

 however, appears to have been exceptionally steady. 



The transits (abstracted in Table IY.) have been reduced in the manner 

 described in the Introduction to the Honolulu Observations. Imperfect 

 transits have been reduced to the center wire by means of the equatorial 

 intervals given above. 



The stars observed for clock-error were taken from the Nautical Almanac 

 for 1874 or 1875. The Mean Right Ascensions are taken from the Greenwich 

 Catalogue of 2760 Stars for the Epoch 1864, the reductions from mean to 

 apparent place being taken from the Nautical Almanac. 



For the determination of azimuth-error, Mr. Stone's Catalogues of 

 8 and 78 Southern Circumpolar Stars were used. The mean places for 1874, 

 January 1, have been given in Part III., page 356. 



The true clock time of transit of the Moon's limb in the eighth column 

 requires a further correction of O s< 02 for diurnal aberration. 



The transits of stars selected for publication are those observed in con- 

 nection (1) with every observation of the Moon for absolute longitude; 

 (2) with chronometric differences of longitude ; (3) with the actual Transit 

 of Venus. 



The abstract of Table V. contains the Errors and Rates of the Transit 

 Clock, the errors being corrected for the approximate values of the personal 

 equations, assuming Mr. Sidgreaves (WS) as the standard. The clock's 

 loss in 24 hours corresponds to the middle time between the two sets of 

 observations from which it has been deduced ; the adopted rate corresponds 

 to the approximate sidereal time given. When the interval of time for 

 which clock-rate has to be allowed in determining the sidereal time for any 

 purpose exceeds six hours, the " loss in 24 hours " has been used as the rate. 



For reasons before mentioned, the clock-error cannot be considered certain 



