PREFACE. 
The geographical knowledge of the colony being so very imperfect, and 
only two partial maps in existence that could at all be depended on ; one, 
that of De la Rochette already noticed ; the other, a survey on a very large 
scale, having all the farms marked down from Zwellendam to Algoa Bay, 
and from the first chain of mountains to the sea-coast, comprehending, 
however, only a small portion of Zwellendam, Lord Macartney, in the 
instructions I had the honor to receive from him, enjoined me to pay a 
particular attention to this important subject. I furnished myself, accord- 
ingly, with a sexant of six inches radius, by Ramsden ; an artificial hori- 
zon ; a good pocket chronometer ; a pocket compass ; and a measuring 
chain. Having been able, in the course of a few days, to ascertain pretty 
nearly the usual rate of travelling with waggons drawn by oxen, I care- 
fully noted down the time employed from one halting place to another, 
with the direction of the road, as pointed out by the compass. 
The uniform pace of the oxen, the level surface of the great Karroo or 
desert, and the straightness of the road, were data that might alone have 
supplied a sketch of tolerable exactness ; but, in order to ascertain any little 
deviation that might have been made, either to the northward or the south- 
ward, a meridional altitude of the Sun was regularly taken every day, the 
constant clearness of the weather being favorable for suqh observations. 
A series of latitudes thus obtained, at intervals of about twenty miles of 
distance, supplied a correction by which the route might be reduced to a 
great degree of certainty. 
The stations or resting-places of each day being verified by these means, 
I then took the bearings, and made intersections, of any remarkable point 
in the distant mountains, as long as it could be seen, for the purpose of 
determining its position upon the chart. The uninterrupted lines, in which 
the chains of mountains generally run on the south part of the continent 
of Africa, are particularly favorable for laying down a sketch of the coun- 
try, without going through the detail of a regular survey. 
