fpiral horns are three feet in length, and feem to be very ill
adapted for the convenience of the animal in the thick covert
which it oonftantly frequents. The hind part of the dufky
moufe-colored body has feveral clear white ftripes, and different
from moft o f the genus: on the neck is a fhort mane : the
ileih is dry and without flavor.
The beds of fand, upon the margin o f the valley, were a l
covered with faltpetre as white as fnow. The produ&ion of
this fubftance has certainly an influence upon the temperature
o f the air, caufing a confiderable degree of cold. A full hour
after the fun had rifen the thermometer flood, in the ihade, at
26°, or fix degrees below the freezing point. At Little Loory
fonteyn, where the foil was hard, dry, and ftoney, it was ten
degrees above freezing; and about the fame time on the preceding
morning, on the banks o f the Traka, where there was
alfo much nitre, the mercury was five degrees below the freezing
point. The weather during the three days was perfectly
clear, and the wind had not Qiifted a point. That the
great changes in the temperature of the air upon the defect,
whilft the weather apparently remains the fame, arife from
fiome local rather than general caufe, is pretty evident from another
circumftance: in travelling at night upon the Karroo, if
the wind fhould happen to blow upon the fide, it is very common
to pafs through alternate currents o f hot and cold air
whofe difference o f temperature is moft fenfibly felt. Whether
the cooler columns o f the atmofphere may have been owing to
the fubjacent beds o f nitre, which frequently occur on the Karroo
plains, or to fiome remoter caufe, I have no grounds fiufliciently
eiently ftrong to determine; but a variety of cireumftances
feem to favor the former fuppofition.
In looking through the exhalations of thefe beds o f nitre, a
meteorological phenomenon, of a different nature, was alfo here
accidentally obferved. In marking about funrifie the bearing
by a eompafs of a cone-fhaped hill that was confiderably elevated
above the horizon, a peafiant well acquainted with the
country obferved that it muft: either be a new hill, or that the
only one which flood in that direction, at the diftance o f a
long day’s journey, muft have greatly increafed o f late its di-
menfions. Being directed to turn his eyes from time to time
towards the quarter on which it flood, he perceived, with
amazement, that, as the day advanced, the hill gradually funk
towards the horizon, and at length totally difappeared. The
errors o f fight, occafioned by the refractive power o f the air,
are fo Angular, and fometimes fo very extraordinary, as
hitherto to have precluded the application of any general
theorem for their correction, as it is not yet afcertained even
through what medium rays of light, in their pafiage, fuffer
the greateft and leaft degree of refraCtion. Were this precifely
known, obfervations on the fubjeCt might lead to a more intimate
knowledge o f the nature of the different currents of air
that float in the atmofphere, and without doubt are the caufe
of extraordinary appearances o f objeCts viewed through them,
A; gentleman, to whom the world is much indebted for his
many ingenious and ufeful inventions and difcoveries, once
propofed to determine the refractive power o f different liquids
and aeriform fluids; and it ia to be hoped he ft'ill means to
p 2 profecute