LATITUDE, AND LONGITUDE FROM ZENITH DISTANCES. 359 



Observer. J I. Number of Obs. D II. Number of Obs. Mean Longitude, 



s s h m s 



B 43-z5 4 42-02 4 4.13.42-63 



H 3g-88 5 46-36 4 4.13.43-11 



N 37-40 i 43-77 4 4.13.40-59 



MEAN, POINT VENUS EAST of GREENWICH 4. 1 3. 42-1 1 



(2.) Longitude of Point Venus, from the observed Zenith Distances of the Moon. 



Kodriguez is not very favorably situated for the application of this method 

 in the autumn months, the ecliptic being far from perpendicular to the 

 horizon at the times at which the Moon can be observed, and difficulty was 

 experienced in obtaining a sufficient number of observations of the Moon's 

 second limb. 



The method of comparing the Altazimuth Clock with the Transit Clock, 

 and of making and of reducing the Zenith Distance Observations, have been 

 described in the Honolulu section. The corrections to the Moon's Tabular 

 R. A. and N. P. D. were taken from the Appendix. 



It was not the general practice at Point Venus to observe the vertical 

 transit of a star near the Moon. The time, determined by one observer with 

 the Transit instrument, was transferred to the Altazimuth Clock, and was 

 used by another observer. 178 zenith-distance observations were made on 

 28 days. For each observation, the Tabular Zenith Distance was computed 

 from the Nautical Almanac with corrected elements (as explained in the 

 Appendix) on the two assumptions of longitude 4 h . 13 m . 10 s . and 4 h . 14 m . s . 

 East of Greenwich. The comparison of these gave a longitude of the station. 

 An abstract of these results is given in Table VII. 



The differences between the Observed and the Tabular Zenith Distances of 

 the stars observed in vertical transit are collected in the following table. 

 The series is sufficiently numerous as regards the comparison of times deduced 

 from Mr. Burton's Altazimuth Observations with times given by Lieutenant 

 Neate's Transit Observations, and shows a large systematic discordance. 



There is some slight evidence of a similar discordance of opposite sign 

 between Lieutenant Neate with the Altazimuth and Lieutenant Hoggan with 

 the Transit ; but, neglecting the single comparison on October 2, there are 

 no observations for estimating the amount of the discordance for the other 

 four combinations of observers and instruments. It is somewhat singular, 

 in view of the certainty of the existence of these systematic errors, that the 

 mean longitude by Altazimuth should be so very near to the mean by the 

 Transit instrument. 



