CLOUD-OUTLINES. 
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occupying the upper stratum .* Some of the masses of cumulus 
will be observed to throw off limbs or projections which swell 
out, and, ascending almost to the upper drift, seem to creep 
over the zenith much in the manner of a thunder-cloud when 
the electricity is gathering just over the place of observation. 
The cloud then forms into a kind of sheet (as seen from below) 
with rounded outline, and the edge broken with many small, 
curling indentations, somewhat like the leaves of several plants. 
The lower portion has a flat appearance, as if repelled, rather 
than attracted, by the earth. The elevation is considerable, and 
the tint of the cloud a dirty grey or slate-colour. 
This kind of cloud frequently forms in enormous masses, as 
may be seen from its great altitude and the manner in which it 
spreads out towards the horizon ; but, though much flatter in 
form than most varieties of cumulus, its surface is often broken 
or nodulous, like that of hail cumulus or electric cumulus when 
these are ready to discharge their contents. The peculiar form 
of the species we are considering is probably due in part to the 
saturated condition of the lower atmosphere at the time of its 
occurrence ; and I have given to it the special designation of 
“ rain ” cumulus to indicate the excessively wet weather that 
it is generally associated with. 
One of the most remarkable facts in connexion with atmo- 
spheric phenomena is this — that certain characteristic forms of 
cloud find their habitat within a certain zone, or at certain dis- 
tances from the earth’s surface. Taking the three main types 
(and omitting stratus), we find them usually in the following 
order, ascending from the earth : 1. Cumulus. 2. Cirro-cumulus, 
3. Cirrus. The second of these appears to be an intermediate 
stage between cirrus, the ice-cloud in its normal state, and 
cumulus ; or between cirrus and nimbus ; and it has a very 
great range of altitude. Thus it might appear to be an excep- 
tion to the law, that form depends partly on elevation ; but it 
will, I think, be admitted that, as a general rifle, it occupies a 
region lying between that of the other two species. But there 
are doubtless relations existing between the banks of cloud 
themselves which affect the question of form, as well as mere 
height above the earth. This especially would be the case where 
there was strong interchange of electrical action. 
But whatever may be the cause of the fact we speak of, one 
thing in connexion with it deserves attention, viz., that any 
decided deviation from the law is significant of a disturbed con- 
dition of the atmosphere, and may be indicative of approaching 
storms. Let us take two cases to illustrate this : In very 
thundery weather, the two great types of cloud show a tendency 
* See remarks below on the relative height of different species of cloud. 
