132 Mr. Colebrooke’s Meteorological Observations 
risen or rising, may be expected to be condensed and made 
visible at an elevation, where the appropriate temperature, con- 
sonant to the height, is so much less than below, as is the 
amount of dryness. In mountainous countries, accordingly, 
the altitude, at which clouds are perceived enveloping summits 
or sides of mountains, may serve fora hygrometric measure, and 
is no bad one. 
With drift-clouds, such as have been mentioned, both scud 
beneath and quiescent clouds above, are not uncommonly 
wanting ; or these are present, and scud only is deficient. 
In cloudy weather, when the upper sky is at any time disco- 
vered through breaks of the extended stratus, a bed of diffused 
fibrous clouds (cirrhi) shews itself. The intermediate series 
of denser clouds is at times wanting between that bed of light 
stationary louds and the low fleeting scud. 
At other times, and in boisterous weather in particular, sta- 
tionary clouds are perceived, seemingly at little elevation above 
the drifted clouds ; suddenly they appear, increase for a while, 
and then wane and vanish without change of place. They are 
produced by a stream of damp air traversing a patch of cold 
however derived. 
An overcast sky occurs sometimes without distinct drifted 
clouds. The extended sheet, in this case, which is of not rare 
occurrence, belongs to upper passing air; the vapour of a su- 
perior damp stratum is condensed at the surface of contact 
with an inferior colder stratum over which it passes; and the 
observable dryness of which satisfactorily accounts for the 
elevation of the sheet of cloud above it. 
Drift clouds, that disperse rain, especially the scanty 
spurts of it attendant upon squalls, are derived from an upper 
stratum of moist air. They here and there sweep the sea’s 
surface, traversing a lower atmosphere, the hygrometric indi- 
cations of which are apparently not quite consistent with their 
presence in it. Observations are continually showing several 
degrees of dryness, while showery squalls recur frequently, and 
are even actually passing. 
In general descending dreft-clouds hang lower than ascending 
