CHAPTER II. 



RATES OF CHRONOMETERS. 



In giving the rates of the Chronometers of the Expedition in the 

 table hereto annexed, I have adopted the true rates, as derived from 

 the observations from time to time during the cruise. These have 

 been established through a daily comparison with one chosen as a 

 standard, and on which the astronomical time was immediately 

 brought from the observatory. Although this chronometer, No. 1567, 

 was selected for this purpose principally for its loud and distinct beat, 

 as well as its being a weekly one, and therefore not liable to the daily 

 winding which those of 56 hours require, yet throughout the voyage 

 it proved itself admirably adapted, not only for the uses it had been 

 selected for, but, as will be seen, maintained a very uniform rate. It 

 was wound every third day, as I felt satisfied its motive power would 

 exert a more uniform motion if confined within the limits of its 

 greatest activity. The chronometers were compared daily on board 

 all the vessels, and every third day, when the squadron was in com- 

 pany, through their standards, with that of the Vincennes, which 

 was entered in the recording books for reference and future use. 

 These were all reduced weekly to mean Greenwich time, from their 

 established rate and errors, and the result of their performances tabu- 

 lated, thus exhibiting at a glance any deviations which might have 

 taken place. The standard has itself been farther corrected by the 

 variation it underwent in each week, after it had become known, on 

 the supposition that its rate had been uniformly increasing or decreas- 

 ing between any two observations or establishments of rate. The true 

 rate thus established has been compared with that of the others, as 

 shown at the weekly comparison, from which has resulted their true 

 rates given in the table, bringing them all to the same test as the 



