240 TRANSIT OF VENUS, 1874. WAIMEA. 



mation Error used throughout is 3" '65, positive with micrometer west. There 

 are a few days when, strictly speaking, a smaller value ought to have been 

 employed, but the fact has no importance, as Mr. Johnson was careful to 

 observe time-stars with both positions of the instrument. The observations 

 of close circumpolar stars were made with the micrometer wire ; the wire was 

 moved successively by quantities equal to one-half or one-quarter of a revo- 

 lution of the screw, and the star then allowed to transit. With Polaris it was 

 Mr. Johnson's habit to record the time when the star's disk seemed to be just 

 touching the wire on both sides. The successive intervals, corresponding to 

 the instants of bisection of the star's disk thus obtained, are not so accordant 

 as those obtained by other observers by the method of estimating the instant 

 of bisection. The number of observations of the circumpolar star, counting 

 the two contacts as one, is shown by a number following the mean micro- 

 meter reading thus "Polaris 8 r> 750 (8)." The observations with the two 

 positions of the transit axis have been separately reduced. On the days 

 referred to above, when a different collimation error should have been 

 employed, they, of course, appear discordant. 



The star's apparent R.A. includes the effect of diurnal aberration. 



The transits selected for publication are those on which depend the 

 difference of Longitude with Honolulu and the Local Time for the Transit 

 of Venus. 



APPROXIMATE LATITUDE of WAIMEA. 



The approximate latitude depends upon the meridian altitudes of the Sun's 

 upper limb, as observed, on 22 days in November and December 1874, by 

 Lieutenant Wellings, with an ordinary navigator's sextant by Whitbread, and 

 mercurial horizon. The Index error of the sextant was determined in the 

 usual way by observing the diameter of the Sun " on " and " off" the arc. 

 The mean instrumental diameter of the Sun was 4" greater than the tabular 

 diameter. No mention is made of the other errors of the sextant, or of the 

 dark glasses employed. The mean of Lieutenant Wellings' observations gives 

 the latitude 



21. 5 7 '-2N., 



which is probably within one minute of the truth. 



LONGITUDE of WAIMEA. 



The determination of the difference of longitude between Mr. Johnson's 

 station and that at Apua, Honolulu, has been described in detail in the 



