THE MIRAGE. 17 
being dried up. Observing what I imagined to be 
a lake at some distance, I proceeded towards the 
spot, but found it merely covered with a saline in- 
crustation, indicating where a brackish pool had 
once been, the water of which had been completely 
evaporated by the sun’s rays, leaving a thin, glit- 
tering crust upon the surface, that produced this 
illusive effect. ‘This remarkable optical deception 
occurs under particular states of the atmosphere, on 
the verge of the horizon, and especially in warm 
climates upon extensive plains. Objects often ap- 
pear with extraordinary elevation, double, or in- 
verted. This singular phenomenon is obviously 
caused by a refraction of the rays of light passing 
through the atmosphere, the lower strata of which 
have different densities. When this effect is con- 
fined to the elevation of an object, the seamen call it 
looming. ‘This singular play of vision has received 
from the French the appellation of mirage.” 
We had still hopes of finding water about eight 
hours’ journey in advance, but that was a long period 
to suffer the misery of suspense; for after all there 
was no certainty of our meeting with a supply; 
and in case of disappointment no other probable re- 
source remained until we should reach the Orange 
River. This made us look forward to the period 
of our arrival in that quarter with considerable 
anxiety. 
VOL. Il. Ni tee 
