LATITUDE OF KAILUA. FORBES' OBSERVATION OF INGRESS. 219 



10 h . 31 m . 26 3 -3 "West of Greenwich. Hence the longitude of the Transit Pier 

 at Kailua is 10 h . 24 m . l s< 7 West of Greenwich. 



LATITUDE of KAILUA. 



The instrument used by Professor Forbes for the determination of the 

 approximate latitude of his station was a repeating reflecting circle by 

 Troughton and Simms, kindly lent by the Royal Astronomical Society. 



Professor Forbes says : " In practice I never used this instrument as a 

 " repeating circle, but simply as an improved form of sextant ; the double 

 " verniers giving greater accuracy and elimin'ating error of centering, the 

 " power of moving the circle bodily being used as a means of varying the 

 " zero-reading. Observations were made only on the Sun about noon. 

 " Previous to a set of observations contacts were made with the limbs of the 

 " two images of the Sun in the same manner as the readings ' off the arc ' 

 " and ' on the arc ' are made with a sextant. This gave the zero-reading 

 " and also a check-observation of the Sun's diameter. Eight or ten observa- 

 " tions of the Sun's double altitude, as reflected from mercury, were made on 

 " each occasion, Lieutenant Noble taking time by the Transit-Clock, or from 

 " a chronometer which was compared with the clock." 



From these observations the latitude appears to be 19. 38' '4 North. 



REPORT of PROFESSOR GEORGE FORBES on his OBSERVATIONS of the INGRESS 

 of VENUS, 1874, December 8. 



Operations at KAILUA, 1874, December 8. 



H.M.S.\Fewed!os, Captain FRED. VAN DER MEULEN, arrived on December 7. 

 Comparisons were made between the Transit-Clock and some chronometers 

 brought for a preliminary longitude-run. 



Captain VAN DER MEULEN told off some officers to take time and assist in 

 the observations ; Lieutenant H. C. BIGGE had been staying at Kailua some 

 time, and the most responsible work was allotted to him. The driving clock 

 of the large Equatoreal was a very imperfect arrangement. It was so 

 irregular in its action (after all care had been taken to make its parts work 

 easily) that it was necessary to have some one well fitted for the work to 

 accelerate or retard the motion slightly, and gently, and to re-connect the 

 clock-work. Mr. Bigge accomplished this admirably. He also attended to 

 the sunshade, clamps, &c. 



F F 



