262 Instructions for 



taining the longitude by a single observation should be con- 

 stantly borne in mind, and the Almanac consulted several days 

 in advance, so that no occultation of a large star certainly 

 identifiable, should be allowed to escape through inadvertence. 



The Committcje especially recommend that every observation 

 made should be registered in a book devoted to that purpose, 

 and preserved in the exact terins of the readings off of the in- 

 strunif-nls and Chronometers, and kept rigorously separate in 

 its statement from any calculation thereon grounded, and that 

 the observed or presumed index or zero corrections, whether of 

 Chronometer, Sextant, Barometer, or other instrument, should 

 be stated separately in every case, and on no account incorpo- 

 rated with observed quantities, and, moreover, that the obser- 

 vations upon which such index errors have been concluded, 

 should also be preserved. Since however the guidance of the 

 expedition will necessitate the calculation of many observations 

 on the spot, the results of such calculations should be entered 

 (as such) beside the observations from which they have been 

 concluded. 



The Committee farther recommend, that the Chronometers 

 with which the expedition has been provided by the liberality 

 of His Majesty's Government, should on no account be cor- 

 rected by moving the hands, however great their errors may 

 become, not even in the extreme case of one or both of them 

 having been allowed to run down. In case of such a misfor- 

 tune (which should be most carefully guarded against by 

 making it the daily duty of more than one person to remind 

 their beareri to wind them at a stated hour) it will be most 

 convenient in place of setting them, to defer winding them 

 until the hours and minutes come round, at which they may 

 respectively have stopped, as near as may be ascertained from 

 one to the other or from both, to other watches of the party, 

 and such event, should it take place, should be conspicuously 

 noted in the observation book ; and, as a further and useful 

 precaution, it is recommended to keep some of the best-going 

 watches belonging to individuals of the expedition, to mean 

 Greenwich time, by frequent comparison with one of the Chro- 

 nometers. In every case where time is observed express mention 

 should be made of the Chronometer or other watch employed, 

 designating it by the maker's name and number, so that no 

 uncertainty may ever arise as to the proper application of the 

 correction for error and rate. 



The rates of the Chronometers should be examined at any 

 station where the expedition may rest two or more consecutive 

 nights, either by equal altitudes of a star or more simply by 

 noticing the disappearance of any large fixed star from the 

 same exact point of view, behind the edge of a board fixed at 

 some considerable distance in the horizon, and having its edge 



