Expedition into Central AJ'rica. 349 



sliould 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 Govern- 

 ment, should on no account be corrected 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 misfortune (which should 

 be most carefully guarded against by making it the daily duty of more than 

 one person to remind their bearers to wini 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 stop- 

 ped 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 jdace, should be con- 

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

 caution, it is recommended to keep some of the best going watches belonging 

 to individuals of the expedition, to mean Greenwich time, by frequent com. 

 parison with one of the chronometers. 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 al- 

 titudes of a star, or more simply by noticing the disappearance of any lai^e 

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

 some considerable distance in the horizon, and having its edge adjusted to a 

 vertical position by a plumb-line; the interval between the two such disap- 

 pearances being an exact sideral day, or 23 h. 56 m. 4 sec. mean time. Under 

 the head of secondary observing stations may be classed those in which no 

 lunar distances can begot, and when the sights for time and meridian alti- 

 tude can only be superficially and imperfectly taken, or one without the 

 other. With a view to the connection of these with the primary station, and 

 to the sketching out a chart of the country passed through, at every primary 

 station a series of angles should be taken with the sextant between remarkable 

 and well-defined points in the horizon, dividing the horizon into convenient 

 portions, and carrying the angles all round the circle, back to the point of de- 

 parture ; and in the selection of such points, two ends should be kept in view 

 first, the precise indentification of the point of observation, incase of its bein-i^ 

 desirable to find it again ; and, secondly, the determination from it of geo- 

 graphical points. The first of these purposes will require angles to be taken 

 between near, the second between distaiU objects. For the latter, of course 

 remarkable mountain peaks will, if possible, be chosen. Of such, when once 

 observed, the ajjjjcarances from the i)lace of observation should be projected 

 by the Camera lucida, and their changes of aspect and form as the expedition 

 advances, should be well and carefully noticed, to avoid mistakes. The ap- 



VOL. XVI II. NO. XXXVI. Al'KII, 1835. A a 



