90 
ESTIMATION OF DISTANCES IN TRAVELLING. 
9 April, 
This greater accumulation of vegetable matter on the southern 
side, is very easily and naturally accounted for, by the relative 
position of the sun in this hemisphere ; which shining at noon, 
always in the north, occasions the northern side of these moun- 
tains, as far as I have had an opportunity of observing, to be always 
the more arid, and producing plants and herbage of less luxuriant 
growth ; while, on the contrary, the southern side, being constantly 
more shaded, and having a cooler aspect, cherishes a rich and ver- 
dant vegetation. Numerous rivulets pour down its ravines, and 
support, in many places, forests of timber trees, whose beautiful 
verdure is preserved through the whole year by the moist atmo- 
sphere which these streamlets, together with shade and shelter, 
create. From the proximity of these mountains to the sea, the 
moisture of marine air may perhaps contribute its influence in pro- 
ducing these effects ; yet I have remarked the same circumstance in 
mountains that are distant from the coast a whole degree of latitude, 
or 90 English miles. * Such a color gives to these streams an 
unpleasant, forbidding aspect ; and the first sight of them recalls to 
mind the dark waters of one of the infernal rivers : Cocytus sinu atro. 
Although a small quantity in a glass vessel, appear limpid and nearly 
colourless, yet, at a depth of three feet, the bottom of a river is not 
visible, and the blackness of the stream gives the appearance of an 
unfathomable pool. This is a disagreeable, and an inconvenience 
not merely ideal ; for, in fording such rivers, a traveller is hereby 
prevented from seeing at the bottom the many large stones and 
holes, which, if not avoided, sometimes occasion serious accidents. 
* In allowing 90 miles of travelling to a degree, instead of 69^, which is its measure 
in a straight line, a result will be obtained much nearer to the truth and more applicable 
to practical purposes, than that obtained by the usual measurement over the face of a map ; 
which last seems to be the method resorted to by those who have hitherto given the dimen- 
sions and distances of places in this colony. From the experiments and calculations made 
in the course of four years' travelling in Southern Africa, I have found the irregularity 
and winding of the roads, and the nature of the surface of this country, to require, on an 
average, a reduction of two-ninths of the distance travelled, to obtain the real horizontal 
distance in a straight line. 
