APrENDIX. 



329 



ments of meridian distances, time was invariably obtained by series 

 of equal, or corresponding altitudes of the sun ; observed by one 

 and the same person with the same sextant, and the same artificial 

 horizon, placed in the same manner, both before and after noon. 



A very good pocket chronometer, carried by hand, in a box, was 

 always used for taking time. In every instance, it was compared 

 with the standard chronometers (the two supposed to be the best) 

 immediately before the morning observation, and again immediately 

 afterwards. It was also compared at noon, and before, as well as 

 after the afternoon, observations. This watch* was so well con» 

 structed, that the intervals shown by it between morning and after- 

 noon observations always agreed with those shown by the standards, 

 (allowing for their respective rates) . 



Generally speaking, seven altitudes of one limb of the sun were 

 taken, and then the same seven altitudes of the other limb, for one 

 set of sights, or observations. Three such sets were usually taken, 

 at short intervals, and the mean result used, unless any marked dif- 

 ference occurred, in which case the result of each separate pair of equal 

 altitudes (morning and afternoon) was computed, and the erroneous 

 ones were rejected. Those were considered erroneous which differed 

 much from the majority. Generally, however, there was the closest 

 agreement between the results of single pairs of sights, as well as 

 between those of entire sets. 



When clouds intervened the series was unavoidably irregular, but 

 the pairs of equal altitudes were always numerous. In a very few in- 

 stances the chronometers were rated by the results of absolute or 

 independent altitudes, taken with every precaution at similar times 

 of day with the same instruments, and by the same observer. In 

 such cases the rates were obtained by comparing together the times 

 obtained by morning observations, or those deduced from afternoon 

 sights ; not by morning and afternoon, or afternoon and morning 

 observations. But the time, considered to be correct, was invaria- 

 bly deduced from equal altitudes, by the method of Professor Inman, 

 At Paramatta, at the Cape of Good Hope, and under the walls of the 

 Koyal Observatory at Greenwich, we had opportunities of trying 

 whether there was any difference between our time, thus obtained, and 

 that of the respective astronomers ; and I feel gratified in being able 



* K, Parkinson and Frodsham. No. 1041 



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