iyG 
of drops which had hern frozen entire in 
fivhr.'T with a rotatory mel on. 
The forms assumed by the suspended wa- 
ter in the ii.ter .al betw een the lirst precipi- 
.tation and tr.a descent or ram, afford a co- 
pious ire id of observation. I hese arc not, as 
night be hastiiy supposed, the sport of 
.wines, changing w ith e very movement of the 
CQtuuimng medium, indeed the atmosphere, 
at the height where clouds usually appear, is 
undisturOeu by the various obstacles which 
throw n i to contending streams and eddies 
near the sunace of the earth,- and flows in a 
ni n e direct and even current. Accordingly, 
the part; v . of water which it contains are 
.allowed to assume a certain arrangement : 
and constitute a form, which is often equally 
well dehned at a distance with that of solids, 
..although, were we to penetrate it, we should 
perceive only the grey mist. 
The e forms have lately been discovered 
to be subject to certain laws in their produc- 
tion, their action on each other, and their re- 
solution into ruin. The visible course of 
these has been traced and described; and the 
antient mode of drawing prognostics seems 
in consequence likely to be restored, with the 
advantage of a nomenclatures by which the 
learned may reason on a subject hitherto, for 
want of terms, in a manner incommunicable, 
and confined to the adepts of experience. 
Before the nomenclature, it will be proper to 
exhibit the general principles on which its 
author proceeds in ins explanation of the 
fasts. 
Evaporation is not a process of solution in 
air, neither is it probable that the water is 
decomposed by it. It is the same procession 
jn the great scale of nature, as in a small quan- 
tity of water placed over the fire. Vapour is 
formed *hd diffused in all directions from its 
source with a force proportioned to the tem- 
perature of tiie water, and subject to the op- 
nosing force of the vapour already in the air. 
The vapour thus emitted may be decom- 
posed in different ways ; as, 1. Immediately 
on its passing into the atmosphere, producing 
a fog or mist. 2. After haying mounted 
through the warm air, near the earth, on its 
arrival in a higher and colder region, in which 
case dense. clouds are there formed. 3. After 
having been uniformly mixed with the mass of 
the atmosphere, and perhaps travelled with it 
to a great distance from its source; in this case 
it eitner falls in dew, or is collected into sheets 
or horizontal beds during a slower subsidence; 
or lastiv, it becomes a conductor to the elec- 
tricity, if the equilibrium of the latter is dis- 
turbed ; and indicates by its arrangement in 
threads, the usual effects of that fluid on light 
bodies. 
In every case, the caloric which constituted 
the vapour decomposed, appears to pass into 
the atmosphere, which hence becomes often 
sensibly warmer just before rain; and on the 
other hand, the evaporation of the water sus- 
pended in the air, robs it of so much as to 
become sensible to our feelings in its compa- 
rative coldness. 
The predisposing causes of these changes 
near the earth are probably to be found in 
the state of the superior currents, which un- 
doubtedly both impart and carry off great 
quantities of vapour; but this part of the sub- 
ject is at present imperfectly provided with 
such observations as might serve for data to 
«mr reasoning. 
M E7F.0H 0 LOGY. 
There are t im e simply and distinct modifi- 
cations, in any one of wnich the aggregate of 
minute drops, cubed a cloud, mav lx- formed, 
increase- to its greatest extent, and Anally de- 
crease: ?.iul disappear. . 
By modification is to be understood simply 
the structure or manner oi aggregation, not 
the precise form or magnitude, "winch indeed 
vape* every moment in most clouds, d ue 
principal modifications are common iy as dis- 
tinguishable from each other as a tree from a 
lull, or the latter from a lake; although clouds 
in the same modification, considered with re- 
spect to each other, have often only the com- 
mon resemblances which exist among trees, 
lid's, or lakes, taken generally. 
The same aggregate, which has been 
formed in one modification, upon a change in 
the attendant circumstances may pass into 
another. 
Or it may continue a considerable time in 
an interned ;ute state, partaking of the cha- 
racters of two modifications; and it may also 
disappear in this stage, or return to the first 
modification. Lastly, aggregates, separately- 
formed in different modifications, may unite 
and pass into one, exhibiting different cha- 
racters in different parts ; or a portion of a 
simple aggregate may pass into another mo- 
dification, without .sep.-.rating from the re- 
mainder of the mass. Hence, together w ith 
the simple, it becomes necessary to admit in- 
termediate and compound modifications, and 
to impose names on such of them as are wor- 
thy of notice. 
The simple modifications are thus named 
and defined : (See Plate Meteorology.) 
1. Cirrus. Def. Nubes cirrata, tenuissima, 
qua? undique crescat. 
Parallel, flex.uous, or diverging fibres, ex- 
tensible in any or in all directions. 
2. Cumulus. Def. Nubes cuinulata, den- 
sa, sur.-um crescens. ■ 
Convex or conical heaps, increasing up- 
ward from a horizontal base. 
3. Strains. Def. Nubes strata, aqua; modo 
expansa, deorsum crescens. 
A widely extended, continuous, horizontal 
sheet, increasing from below. 
The intermediate modifications which re- 
quire to be noticed are : 
4. Cirro-cumulus. Def. Nubecula; densi- 
ores, subrotunda;, et quasi in agmiue appo- 
site. 
Small, well defined, roundish masses, in 
close horizontal arrangement. 
5. Cirro-stratus. Def. Nubes extenuata, 
subconcava vel unduluta. Nubecula; hujus- 
modi apposite. 
Horizontal or slightly inclined masses, at- 
tenuated towards a part or the whole of their 
circumference, concave downward ; or undu- 
lated, separate, or in groups, consisting of 
small clounds, having these characters. 
The compound modifications are : 
6. Cumula-stratus. Def. Nubes densa, 
basim cumuli cum structure patente exhibens. 
A dense cloud with the base of the cu- 
mulus, but in its upper part extended into a 
broad flat structure. 
7. Cumulo-cirro-stratus, vel nimbus. Def. 
Nubes vel nubium congeries pluviam effun- 
dens. 
The rain cloud. A cloud, or system of 
clouds, from which rain is falling. It'is a hori- 
zontal sheet, above which the cirrus spreads. 
’ w hile the cumulus enter! it laterally, and from* 
beneath. 
Q f the cirrus. 
Clouds in this mod i; ation have the least 
density , elevutihn, the great- 
est variety of-- extent and direction. They 
are the earlie. >L appearance, after serene wea- 
iher. 'i hey are first indicated by a few threads 
pencilled, as. it w ere, on the sky. These in- 
civa»e in length, and new' ones are in the 
nTan time added laterally.* Often the first- 
| formed th.eads serve as stems to support nu- 
I melons manCi.es, which in their turn aive 
I rise to others. The process may be compared 
j either to vegetation or to crystallisation; but it 
I is clearly analogous to the* delicate arrange- 
| ments which ensue in the particles of coloured 
; powders, such as chalk, vermilion, &c. when 
tin. ->e ai e projected on a cake oi wax, after- it 
has been touched with the knob of a chanted 
i Leyden phial. We may consider the particles 
of water as similarly placed upon or beneath 
a plate of charged air. 
'J heir duration is uncertain, varying from 
a few minutes after the lirst appearance to an 
extent of many hours. It is long when thev 
! appear alone, and at great heights, and shorter 
j when they are formed lower, and in the vici- 
| nity of other clouds. 
I 1 his modification, although in appearance 
| almost motionless, is intimately connected 
i with the variable motions of the atmosphere. 
Considering that clouds oi this kind have long 
been deemed a prognostic of wind, it is ex- 
traordinary that the nature of this connection 
should not have* been more studied, as the 
knowledge of it might have been productive 
of useful results. 
In fair weather, with light variable breezes ! 
the sky is seldom quite clear of small groups 
of the oblique cirrus, which frequently come 
on from the leeward, and the direction of 
theii increase is to windward. Continued wet 
weather is attended with horizontal sheets of 
tins cloud, which subside quickly, and pass to* 
the cirro-stratus.. ] he cirrus pointing upward 
is a distant indication of rain, and downward a 
more immediate one of fair weather. 1 eff re 
storms they appear lower and denser, and 
usually in the quarter opposite to thai/froqi 
winch the storm arises. Steady high winds 
are also preceded and attended by streaks ! 
running quite across ttie sky in the direc tion 
t hey blow in. These, by an optical decep- 
tion, appear to meet in the horizon. 
The relations of this modification with the 
state of the barometer, thermometer, Jivgro- 
meter, and electrometer, have not yet been 
attended to. 3 
Of the cumulus. 
Clouds in tnis modification are commonly 
of the most dense structure. They are form- 
ed m the lower atmosphere, and move along 
w ith the current which is next the earth. ° 
A small irregular spot first appears, and is 
as it were the nucleus on which they increase. 
The lower surface continues irregularly plane, 
w hile the upper rises into conical or hemi- 
spherical heaps. 
J heir appearance, increase, and disappear- 
ance, in fair weather, are often periodical, and 
kpep p ice with the temperature of the dav. 
1 bus they begin to form some hours after 
sunrise, arrive at their maximum in the hot- 
test part of the afternoon, then go on dimi- 
nishing, and totally disperse about sunset. 
But in changeable weather they partake of 
