FINAL EQUATIONS FOR HONOLULU. 



55 



Colonel Tennant, by similar observations at Roorkee, made this quantity 



+ o"'56 for a 6-inch instrument ; 



and Captain Browne, at Mokattam 



+ o" - 62, also for a 6-inch instrument. 



The following final equations represent the whole of the observations made 

 at Honolulu, omitting the micrometer measures of the distance of Iwibs with 

 the 4^-inch telescope, and the external contact observed with the spectro- 

 scope : 



It is not without interest to compare the times of internal contact, as 

 inferred from micrometric measurements, with the observed telescopic time. 

 Before treating of the measures of the actual transit, I will exhibit the results 

 obtained from the preliminary practice with the model. This apparatus is 

 figured in Plate V., and needs but little description. The shaded portions 

 were cut out of sheet brass ; the curved edges, representing portions of the 

 limb of the Sun and the periphery of the planet, were bevelled to diminish 

 parallax ; the planet, attached to a horizontal bar running on fixed wheels, 

 was drawn towards the clock-work on the right by the action of the large 

 weight, the motion being regulated by a pendulum. 



The curvature of the Sun's edges was such as would be proper for a 

 distance of 400 feet, but at Honolulu the model was erected at the distance of 

 800 feet, the planet being double the diameter shown in the plate. Sunlight 

 was reflected into the telescopes, through the triangular opening, by means of 

 a mirror mounted on another tripod stand, worked by an assistant, who knew 

 perfectly well when it was properly adjusted by the brilliant light reflected 



