246 Mr. Colebrooke on the 
of dryness exhibited by the hygrometer: for temperature de- 
creases with ascent of heights, about 1° of Fahrenheit’s scale, for 
every ninety yards of elevation. 
This will be made plain by citing an instance. Thus, “ on 
11th January, 1822, at Cape-Town ; temperature, 71°; hyg. 
therm. 58°; a cloud hanging over Table Mountain, not touch- 
ing it, but just elevated above the summit. The height of 
Table Mountain, trigonometrically measured, is 1194 yards; 
difference of temperature, according to theory, 131°; degrees 
of dryness observed, 13°. 
“So, on 15th January, at the foot of Table Mountain, tempera- 
ture in the shade during the whole day, (6 A.M. to 44 P.M.), 
70° to 71°; hyg. therm. 59°; wind S.E., strong breeze ; cloud 
on T. M. 
“ Noon, at an elevated station, upon the acclivity, above the 
highest inhabited spot, temperature in wind and sunshine, 69°; 
hyg. therm., 58°. At a station still more elevated, above the 
highest plantations of the silver-tree, (protea argentea,) tempe- 
rature, in ventilated sunshine, 68°; hyg. therm., 584°. 
“« The wind blowing in puffs and gusts, the temperature is 
depressed 4° to 1°, when strong gusts blow. 
«« A dense white cloud on the back of the mountain, receiving 
evidently continued accession. The vapour passing over the 
summit, and scarcely descending a little down the cliff, seeming 
to curl laterally and vertically, and pause while vanishing, as it 
quits the mountain ; sometimes a very small fleece ; often more 
considerable and denser. 
*¢ A small detached cloud shows itself here and there, remains 
a while, and then gradually vanishes; one, over the signal- 
post on the Lion; another, in front of Camp’s-bay; another 
again in the distance, over Tigerberg; all apparently upon the 
same level with the cloud hanging on Table Mountain.” 
The degrees of dryness here indicated, viz., 11° to 12°, agree 
nearly with the elevation of the cloud, between one and two 
hundred yards less than that of the mountain. 
It can scarcely be nevessary to remark, that such hygrometrie 
