the vicissitudes of the atmosphere; sometimes 
evaporating; almost as soon as formed, at 
others suddenly forming;, and as quickly pass- 
ing to the compound modifications. 
The cumulus of fair weather has a mode- 
rate elevation and extent, and a well-defined 
rounded surface. Previous to rain it increases 
more rapidly, appears lower in the atmo- 
sphere, and with its surface full of loose fleeces 
or protuberances. 
The formation of large cumuli to leeward 
in a strong wind, indicates the approach of a 
calm with rain. When they do not disappear 
or subside about sunset, but continue to rise, 
thunder is to be expected in the night. 
Lndependantly of the beauty and magnifi- 
cence it adds to the face of nature, the cumu- 
lus serves to screen the earth from the direct 
rays of the sun ; by its multiplied reflections 
to diffuse, and, as it were, economise the light; 
and also to convey the product of evapora- 
tion to a distance from tne place of its origin. 
The relations of the cumulus, with the state 
of the barometer, &c. have not yet been 
enough attended to. 
It appears that there is a continual evapo- 
ration from the base of this cloud, in conse- 
quence of its tendency to subside into lower 
and warmer air. This evaporation is more 
than compensated during its increase by the 
deposition from above : while the two effects 
balance each other, the cloud remains sta- 
tionary as' to hulk; when the supply from 
above fails, it sinks into the lower air, and 
totally disappears. r I his happens usually a 
little before sunset, because the inequality in 
the temperatures of the higher and lower air, 
by virtue of which it subfisted, gives place at 
that time to the tendency to equal diffusion 
of the caloric. 
Of the stratus. 
This modification has a mean degree of 
density. It is the lowest of clouds, since its 
inferior surface commonly rests on the earth 
or water. 
Contrary to the last, which may be consi- 
dered as belonging to the day, this is pro- 
perly the cloud of night ; the time of its first 
appearance being about sunset. It compre- 
hends all those creeping mists which in calm 
evenings ascend in spreading sheets, like an 
inundation of water, from the bottom of val- 
leys, and the surface of lakes, rivers, Ac. Its 
duration is frequently through the night. - 
On the return of the sun, the level surface 
of this cloud begins to put on the appearance 
ot cumulus, the whole at the same time sepa- 
rating from the ground. The continuity is 
next destroyed, and the cloud ascends and 
evaporates, or passes off with the appearance 
of the nascent cumulus. 
This has been long experienced as a prog- 
nostic of fair weather ; 
At nebulae magis ima petunt, campoque 
recumbunt: — Virgil. Georg, lib. i. 
and, indeed, there is none more serene than 
that which is ushered in by it. The relation 
of the stratus to the state of the atmosphere as 
indicated by the barometer, Ac. appears, not- 
withstanding, to have passed hitherto without 
due attention. 
Of ike cirro-cumulus.. 
The cirrus having continued for some time 
increasing, or stationary, usually passes either 
to the cirro-cumulus, or the cirro-stratus ; at 
VOL. II. 
METEOROLOGY. 
the same time descending to a lower station 
in the atmosphere. 
The cirro-cumulus is formed from a cirrus, 
or from a number of small separate cirri, by 
the fibres collapsing, as it were, and passing 
| into small roundish masses, in which the tex- 
ture ot the cirrus is no longer discernible, al- 
j though they still retain somewhat of the same 
I relative arrangement. This change takes 
| place, either throughout the whole mass at 
j once, or progressively from one extremity to 
j the other. In either case, the same effect is 
I produced on a number of adjacent cirri at 
! the same time, and in the same order. It 
| appears in some instances to be accelerated 
j by the approach of other clouds; and is pro- 
j bably due to the equilibrium of the electric 
fluid between the cloud and the surrounding 
1 atmosphere. 
j This modification forms a very beautiful 
sky, sometimes exhibiting numerous distinct 
beds ot these small connected clouds floating 
at different altitudes. 
The cirro-cumulus is frequent in summer, 
I and is attendant on warm anti dry weather. 
1 It is also occasionally, and more sparingly, 
seen in the intervals of -showers, and in winter, 
i This cloud is a sure prognostic of increased 
' temperature. It may either evaporate, or 
pass to the cirrus or cirro-stratus. 
Of the cirro-stratus. 
This cloud appears to result from the sub- 
sidence of the fibres of the cirrus to a hori- 
zontal position, at the same time that they 
approach towards each other laterally. The 
form and relative position, when seen in the 
distance, frequently give the idea of shoals 
| of fish. Yet in this, as in other instances, 
the structure must be attended to, rather than 
the form, which varies much; presenting at 
other times the appearance of parallel bars, 
interwoven streaks like the grain of polished 
; wood, Ac. It is always thickest in the mid- 
dle, or at one extremity, and extenuated to- 
wards the edge. r ] he distinct appearance of 
a cirrus does not always precede the produc- 
tion of this and the last modifications. 
of subsidence, as in common cases of precipi- 
tation in fluids at rest. 
Of the cumulo- stratus. 
1 he different modifications which have 
been just treated of, sometimes give place 
to each other: at other times two or more 
appear in the same sky; but in this case the 
clouds in the same modification lie mostly in 
file same plane of elevation, those which are 
more elevated appearing through the inter- 
vals ot the lower, or the latter shewing dark 
against the lighter ones above them. When 
the cumulus increases rapidly, a cirro-stratus 
is frequently seen to form around its summit, 
reposing thereon as on a mountain ; while 
the former cloud continues discernible in 
some degree through it. This state continues 
but a short time. I he cirro-stratus speedily 
becomes denser, and spreads; while the su- 
perior part of the cumulus extends itself, and 
passes into it, the base continuing as. before, 
and the convex protuberances changing their 
position till they pr sent themselves laterally 
and downward. More rarely the cumulus 
alone performs this evolution, by the move- 
ment or mode of increase of its superior part. 
In either case, a large lofty dense cloud is- 
formed, which may be compared to a mush- 
room with a very thick short stem. But when 
a whole sky is crowded with this modification, 
the appearances are more indistinct. Tie 
cumulus rises through the interstices of the 
superior clouds ; and the whole, seen as it 
passes off in the distant horizon, presents to 
the fancy mountains covered with snow, in- 
tersected with dark ridges and lakes of water, 
rocks and towers, Ac. The distinct cumulo- 
stratus is formed in the interval between the 
first appearance of the fleecy cumulus and 
the commencement of rain ; also during the 
approach of thunder-storms. The indistinct 
appearance of it is chiefly in the longer or 
shorter interval of showers' of rain, snow, or 
hail. 
The cumulo-stratus 'chiefly affects a mean 
state ot the atmosphere, as to pressure and 
temperature, but is not peculiar to any sea- 
son; and it may be seen before a fall of snow, 
as well as before a thunder-storm. 
! The cirro-stratus precedes wind and rain, 
the near or distant approach of which may 
sometimes he estimated from its greater or 
less abundance and permanence. It is almost 
I always to be seen in the intervals of storms 
Sometimes this and the cirro-cumulus appear 
together in the sky, and even alternate with 
: each other in the same cloud, when the dififer- 
. ent evolutions which ensue are a curious 
spectacle; and a judgment may be formed of 
the weather likeiy to ensue, by observing 
j which modification prevails at" last. The 
( cirro-stratus is the modification which most 
frequently and completely exhibits the phe- 
nomena of the solar and lunar halo, and (as 
I supposed from a few observations) the par- 
helion and paraselene also. Hence the rea- 
■ son of the prognostic for foul weather com- 
: monly drawn from the appearance of halo, 
i This cloud is among those natural indications 
i which may be trusted in confirmation of the 
j indications of the barometer and hydrometer 
for rain. It may be reasonably thought to 
originate from a supervening cold and moist 
current, occasioning precipitation in the atmo- 
sphere below, before it is itself to be perceived. 
Its appearance often indicates the simple act 
Z 
OJ the nimbus, or cumulo-cir ro-stra tus. 
Clouds in any one ot the preceding modifi- 
cations, at the same degree of elevation, or 
two or more of them, at different elevations, 
may increase so as completely to obscure the 
sky, and at times put on an appearance of den- 
sity, which to the inexperienced observer in- 
dicates the speedy commencement of rain, 
it is nevertheless extremely probable, ah well 
from attentive observation, as from a consi- 
deration of the several modes of their pro- 
duction, that the cjouds, while in any one of 
tiiese st&tes, do not at any time let fall rain. 
Before this effect takes place, th»y have 
been uniformly found to undergo a change, 
attended with appearances sufficiently re- 
markable to constitute a distinct mortifica- 
tion. These appearances, when the rain hap- 
pens over our heads, are but imperfectly 
seen. We can then only observe, before the 
arrival of the denser and lower clouds, or 
through their interstices, that there exists at 
a greater altitude a thin light veil, or at least 
a hazy turbidness. When this has consider- 
ably increased, we see the lower clouds 
spread themselves till they unite in all points, 
and form one uniform sheet. Tiie rain then 
