46 



TRANSIT OF VENUS, 1874. HONOLULU. 



have rotated the' micrometer to place the head in a more convenient position, 

 as I was at that time ignorant of the fact that this form of micrometer is 

 liable to a variation of its zero as it is rotated about its axis. The measures 

 of limbs, however, are practically independent of the zero, while for the 

 cusp-measures the zero was determined immediately before them with the 

 micrometer in its proper position. 



The Sun was now approaching the western horizon. Lieut. Ramsden had 

 secured 60 photographs, Mr. Nichol a series of micrometric-measures similar 

 to my own, and Lieut. Noble the telescopic contact. The clocks and chrono- 

 meters were then compared. Every observer made his notes in full before 

 any conversation passed between us, and wrote his Report, as here given 

 with no material alteration, the same evening. 



TABLE A. COMPARISONS of the TRANSIT and EQUATOREAL CLOCKS by intervention 

 of the SOLAR CHRONOMETERS R AND C and inferred ERROR of the 

 EQUATOREAL CLOCK, 1874, December 8. 



I now proceed to the discussion of these observations in order to put 

 them in the form of final equations immediately available for the determina- 

 tion of the solar parallax, which was the special object of the Expeditions ; 

 premising that every observation resolves itself into a measure in a direction 

 joining the apparent centers of the SUN and VENUS, as seen from the place 

 of observation, and that the formulas by which the local tabular distance of 

 centers and the various co-efficients have been computed, were taken from 

 the Astronomer Royal's paper in the Monthly Notices of tlie Royal Astronomical 

 Society, Vol. XXXV., 277, the geocentric places of the SUN and Venus being 

 taken from the ephemeris for every 10 seconds of Greenwich sidereal time 

 computed from LEVERRIER'S Tables by direction of the Astronomer Royal. 



