26 TRANSIT OP VENUS, 1874. HONOLULU. 



shade in the open air, close to the altazimuth hut. The temperature of the 

 column of mercury was therefore sensibly the same as that of the external 

 air as indicated by the verified thermometer suspended on the north side of the 

 altazimuth observatory, the readings of which are inserted in the same column. 



Column 9 contains the refraction computed as described on page 21. It is 

 additive to the circle-reading when the lamp is " left." 



Column 10 contains the true observed zenith distance obtained by applying 

 the zenith point given at the bottom of the page to the circle-reading 

 connected for level and refraction. 



Column 11 contains the Greenwich Mean Solar Time corresponding to 

 the (slightly inaccurate) local sidereal time of observation on two 

 assumptions of the longitude, viz., 10 h . 31 m . O and 10 h . 32 m . s West of 

 Greenwich. 



The Tabular Geocentric Right Ascension and North Polar Distance of the 

 Moon's center, given in the twelfth and thirteenth columns, have been inter- 

 polated with second differences from the hourly ephemeris in the Nautical 

 Almanac, and have been corrected for errors of the tables by the quantities 

 given in the Appendix. The corrections applied are not absolutely identical 

 with those used for the Moon culminations, but the difference is unimportant, 

 as explained in the Appendix. 



The Moons Equatorial Horizontal Parallax and Semidiameter have been 

 interpolated from the 12-hourly ephemeris. 



The Tabular Zenith Distance in the seventeenth column has been computed 

 by the normal-centric method, from the formulae given at length in the 

 introduction to recent volumes of the Greenwich Observations (Section Altazi- 

 muth Observations). The hour angle is shown in the sixteenth column. 



The eighteenth, column contains the longitude as inferred from a comparison 

 of the two tabular zenith distances of the limb of the Moon with the observed 

 zenith distance in column 10. This longitude is subject to future correction, 

 in consequence of the original error in the local sidereal time as explained 

 above. The difference between the two tabular zenith distances corresponding 

 to the local sidereal time of observation affords the measure of the value of 

 the observation. 



66. Table XI. contains the Altazimuth results for each day. Each result 

 is corrected, and all are combined with the assigned weights to form the 

 mean. 



The correction in the fifth column is on account of the difference of 

 longitude between the transit and altazimuth piers, which was neglected in 

 forming the table of corrections of the altazimuth clock. It is thus 

 computed : 



