36 TRANSIT OF VENUS, 1874. HONOLULU. 



ATTEMPT TO CONNECT HONOLULU WITH SAN FKANCISCO. 



81. H.M.S. Reindeer, Commander C. V. ANSON, R.N., was to convey the last 

 of the party from Honolulu to San Francisco, and as it was probable that, 

 at that season of the year, she would carry westerly winds all the way and 

 make a short passage, it was resolved to employ the chronometers to measure 

 the meridian distance. Her departure from Honolulu was fixed for March 20. 



82. The errors of the chronometers were determined by observations of the 

 Sun, with a reflecting circle by Troughton and Simms divided to 20" and 

 read by three verniers, the Sun's rays being reflected from mercury under a 

 cover of glass in the usual manner to obtain the double altitude. 



Mr. Noble called the seconds from the sidereal chronometer N, which was 

 chosen on account of its loud beat, distinctly audible to the observer with 

 the circle. Five double altitudes of one limb were taken, the circle and the 

 cover of the mercury trough were then reversed, and five double altitudes of 

 the other limb taken, all three verniers being read each time.* The chrono- 

 meter N was compared, by coincidence of beats, with the two solar 

 chronometers Q and R (which were not disturbed) before and after every 

 set of observations, and thus the observations gave the errors of these three 

 chronometers with equal accuracy. The errors of the others were obtained 

 by comparing them in the usual way with N, Q, and R, about noon each day. 

 The habits of observing and comparing were exactly similar at Honolulu and 

 at San Francisco, to avoid systematic errors. The Sun was observed 3 h or 4 h 

 from the meridian in the morning and in the afternoon. It will be sufficient 

 to give as an example the actual observations made on one day ; for instance, 

 those on 1875, March 9, Table XVI. The circle reading in the ffth column is 

 the mean of the three verniers. The index correction was found to be 22", 

 additive when the circle was read backwards. The N.P.D. of the Sun and 

 the equation of time have been interpolated from the Nautical Almanac for 

 the mean of the five recorded times, assuming the longitude to be 10 h . 31 m . 14 s 

 west. The refraction has been computed, for the mean of each five observed 

 altitudes, from the Greenwich Tables. The semidiameter employed is the 

 mean of all the daily measurements. 



83. Table XVII. is an abstract of all the errors obtained before leaving 

 Honolulu. Table XVIII. is a similar abstract of errors obtained at Mare 

 Island, San Francisco, where the Reindeer arrived on the morning of April 9. 

 Instead of making a short passage under favorable circumstances, she was 



* The darkening glass fitted to the eyepiece of the telescope was always used. 



