122 Mr. Colebrooke’s Meteorological Observations 
ture. Its agitation, and wind passing over it, tend to main- 
tain a more nearly uniform heat. 
The point, at which deposition of dew takes place, is more 
stable than that of the temperature of air. It fluctuates scarcely 
more than a degree in course of the day, unless upon occasion 
of a sudden or violent change of weather. Very few such in- 
stances occurred to notice : and variations in degrees of dryness 
are more owing to diurnal alterations of temperature in the 
atmosphere, than to changes of that at which vapour becomes 
condensable. Evidence of this fact recurs at every turn. 
The utmost degree of dryness observed in the atmosphere 
over the sea, either with a ¢trade-wind, or with a north breeze 
in the northern Atlantic, or a south wind in the southern, has 
been nearly one-third of the air’s capacity for moisture: (.30 to 
-31 centisimals.) The maximum on shore, in South Africa, as 
actually observed upon the sea-coast, has been twice as much. 
A greater degree of dryness was experienced at inland stations ; 
but instruments were not at hand to determine its precise 
quantity. 
The minimum was of course, both on sea and on land, the 
point of saturation with moisture, or zero of dryness: which, 
however, rarely occurred ; and only in mists or continued rain, 
or stormy and wet weather. 
The temperature of the mid ocean is lower than that of seas 
nearer to land. In this respect, the influence of the continent 
of Africa, appears to extend as far as to the clusters of islands 
which lie at considerable distance off its shores; or those 
islands have themselves a sensible influence over the seas around 
them. 
A month after the autumnal equinox, the sea and atmosphere 
over it, in the yicinity of the Madeira islands, exhibited a mean 
of 73°; viz., air, 72°; water, 74° to 731°. But, near the sum- 
mer solstice, in the same parallel of latitude, at a distance of 
more than three hundred leagues west, the temperature was 
69°; wvig., air, 67° to 69°; water, 69° to 70°. 
Near the Canary islands and Palma island in particular, at 
o] 
