350 Expedition into Central Africa. 



proximate diatance of any remarkable object may be had by pacing or other- 

 wise measuring more exactly, a base line of a few hundred paces, in a direc- 

 tion perpendicular to that in which it appears, erecting a staff at each end, and 

 from each staflf measuring the angle between the object and t,he other sta€F. 



"In this manner the neighbourhood of any station may be mapped down so 

 as to be available for many usefiil purposes. In all such cases the compass 

 bearings of the most important object in the horizon should be taken, and in 

 the absence of the sextant angles, azimuth 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 various 

 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 distance and 

 bearing by compass of the bottle, from its centre, and that the situation of 

 such places of deposit should also be ascertained by exact compass bearings of 

 several 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 or that of future 

 travellers. 



" In surveying the basin of a river, or in proceeding along the prevailing 

 slope of a country, it is very desirable to determine as many points as pos- 

 sible on the same level, and form thus as it were a parallel of elevation to 

 the level of the sea. A line of this kind traced at the altitude of, say 1000 

 feet, would determine, in a considerable degree, the physical condition of ex- 

 tensive spaces on the map on both sides of it. The stations of most interest 

 will be found at the extremities 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 rate and 

 direction ; and in regard to the valleys 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 investiga- 

 ted, along with the nature of their climate and of the clouds formed upon 

 them. It will be requisite also to mark with care the nature of the winds 

 and sky, 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 appear- 

 ances as indicate or accorrpany changes of structure in the formation, or of 

 components in the soil and surface, especially such fossil remains of plants or 

 animals a.s may occur, and metallic ores, and that proper specimens accom- 

 pany these notes, ticketed on the spot with precise localities. 



