in a Voyage across the Atlantic. 131 
Over them, other beds of clouds are very usually seen, 
passing in directions different from that of the wind. 
Above all, is a stratum of clouds at rest. 
Over the sea, these distinct strata of clouds are in general to 
be seen; or, when the layers are more numerous, they seem to 
be reducible to those three primary distinctions. Heaps of 
dense, woolly or cottony vapour, at various elevations, are driven 
by upper currents of air, not uncommonly deviating from the 
direction of the wind, which is the lowest current. Fleecy scud 
passes beneath, with the wind; or sometimes not quite conform- 
ably ; and often scattered at more than one level, exhibiting 
variety of density : scud lowest; cleser fleeces above that; and 
looser over them; marking the difference of their height by the 
unequal velocity with which they pass. Fibrous clouds hang 
over all, and remain. at rest; manifesting intestine commotion, 
indeed, but no progressive movement. 
In dry and fair weather, a serene sky presents none, but of 
this last mentioned character: cirrhi, or cirrhostratus of Mr. 
Howard’s nomenclature. 
They appear in this case to correspond with the observed 
hygrometric state of the accessible atmosphere; its dryness seems 
to account satisfactorily for their elevation. Vapour descending 
lower than the limit which that prescribes is dissolyed, and be- 
comes transparent; it ceases to be cloud. 
Their source probably is warm humid air, still higher. Vapour, 
thence condensed upon the surface of contact, descends until it 
is re-dissolved. The intermediate space is occupied by cloud ; 
seemingly at rest. 
Dilute and fibrous clouds are seen at great elevation, when 
the air marks much dryness. 
Diffused splashes, and pencilled streaks, compact but shal- 
low, belong to less height, and less atmospheric dryness; but 
equally stationary, they appear to have a like origin. 
Oftener, even in fair weather, attended however with a mean 
degree of humidity, dispersed heaps of dense vapour /cumuli) 
are seen drifted in the middle atmosphere, at a height appa- 
rently not unsuited to the observed degree of dryness. Vapour, 
Vor. XIV. ind. 
