OBSERVATIONS FOR LATITUDE. 21 



which, under the able management of Professor W. D. ALEXANDER, had 

 already made great progress when the Expedition visited the Islands. The 

 stars selected were such as had been well observed in N.P.D. either at 

 Greenwich, the Cape of Good Hope, Melbourne, or Oxford, and were equally 

 distributed north and south of the zenith of Honolulu. Table VII. contains 

 the adopted places of the stars and the separate determinations of N.P.D. 

 that have been used. For stars south of the Equator a preference has 

 been given to the N. P. D.'s determined at the Cape Observatory and at 

 Melbourne. 



54. The observations for co-latitude are shown in the Table VIII. The 

 fourth column contains the time by the Altazimuth Clock, when the observer 

 bisected the star with the middle part of the center horizontal wire, by 

 turning the fine zenith-distance slow-motion screw. The error and rate of 

 the clock have been given (Table VI.). The fifth column shows the position 

 of the instrument, by the illuminating-lamp being on the observer's right or 

 left hand as he faced the star. The sixth column contains the concluded 

 circle-reading as obtained from the mean of the four microscopes corrected 

 for runs. The seventh column contains the level indication, which is one half 

 of the sum of four readings corresponding to the ends of the bubbles ; for 

 each level had 30 divisions to the minute. 



The refraction in the eighth column has been computed from the Tables of 

 Bessel's Refractions in the Appendix to the Greenwich Observations, 1853, 

 and then multiplied by the factor O9947. [Mr. Stone, Monthly Notices of the 

 Royal Astronomical Society, 1867, November 8]. 



55. The Mercurial Barometer, A. 2 Casella No. 352, and External Thermo- 

 meter were tested at the Royal Observatory, Greenwich, and were found to 

 have no sensible errors. The former was suspended under the thatched 

 covering of the East Collimator, where the temperature at night, as indicated 

 by the attached thermometer, was always from 1 to 2 higher than the 

 external air. The latter \vas attached to the north side of the Altazimuth 

 hut, about four feet from the ground. The readings are given in the ninth 

 column. 



56. The observed zenith point in the tenth column is thus found : if C,, C r 

 be the circle-readings for the same object, corrected for level and refraction, 

 with the lamp left and lamp right respectively, and r l5 r a the corresponding 

 reductions to the meridian, the zenith point is ^ (C, t\ -f- G r + r 2 ). 



The concluded zenith distance in the twelfth column is the difference 



D 2 



