1835] 



Expedition into Central Africa, 



In this manner the neiglibaur hood of any station may mapped 

 down so as to be available for many useful purposes. In all such 

 cases the compass bearings of the most important object in the hori- 

 zon should be taken, and in the absence of the sextant angles, azi- 

 muth compass readings of each point may be substituted, though of 

 course with less precision. 



Indications of the progress of the expedition should be left at va- 

 rious points in its course by making marks on rocks or stones, &c. 

 ^and by burying documents in bottles. In regard to the latter it will 

 be necessary to deposit them one foot deep at some known distance, 

 say 15 feet from a conspicuous surface of stone, on which there is 

 painted a circle containing the distfince and bearing by compass of 

 the bpttle, from its centre, and that the situation of such places of 

 deposit should also be ascertained by ex ict compass bearings of seve- 

 ral remarkable points in the horizon, both near and distant, as well 

 as by angles between them, carefully determined with a sextant, and 

 noted down in the journals of the expedition for their own reference 

 x)r that of future travellers. 



In surveying the basin of a river, or in proceeding along the pre- 

 vailing slope of a counlry, it is very desirable to determine as many 

 points as possible on the same level, und form thus as it were a pa- 

 rallel of elevation to the level of the sea. A line pf this kind traced 

 at the altitude of, say 1000 feet, would determine in a considerable 

 degree the physical condition of extensive spaces on the map on both 

 sides of it. The stations of most interest will be found at the ex-^ 

 tremities of transverse arms of the ridge, or in the central and most 

 retiring points of the intervening spaces. Let the general slope of 

 the country on both sides of such stations, be noted as to its rat« 

 and direction ; and in regard to the vailies which intersect the slope, 

 let their width, direction, and general rate of declivity, and the section 

 and velocity of their streams, be ascertained, and the probable course 

 of the rivers, as far as it can be determined by the appearance of the 

 . country, and the reports of the natives ; giving them the aboriginal 

 names when they can be discovered. The altitude and acclivity of 

 remarkable peaks or ridges should also be investigated, along with 

 the nature of their climate and of the clouds formed upon them. It 

 will be requisite also to mark wdth care the nature of the- winds and 

 skv as well as the temperature at stations in the neighbourhood, and 

 to note the influence which changes of that description have upon 

 the barometer, and observe also the temperature of deep pools or 

 lakes and copious springs. 



The geological structure of the country is especially worthy of 

 minute and extended observation, and will require that notes be 

 kept of all such appearances as in licate or accompany changes of 

 structure in the formation or of components in the soil and surface, 

 especially such fossil remains of plants or animals as may occur, 

 and metallic ores, and that proper specimens accompany these notes, 

 ticketed on the s^'Ot v/ith precise localities. 



