the earth is also probably less frequent than 
i from cloud to cloud. 
'idle far greater part of the visible pheno- 
mena of the atmosphere are due to the wa- 
ter which, being raised by evaporation, is 
transported from place to place in vapour, 
| and which, physically speaking, is a proper 
component part of the air. W hen by any 
means a portion of this is deprived of its con- 
’ stituent caloric, it reappears in minute drops, 
j which are at first uniformly diffused, and 
I lessen the transparency of tiie air in propor- 
| tion to their abundance. By the report of 
J those who have ascended the highest moun- 
1 tains, or performed aerostatic voyages, there 
! is usually a sufficient quantity of this diffused 
: water, especially towards evening, to become 
; visible from above as a sea of. haze, it should 
J seem that this is, in fact, the veil which, 
! being drawn over the sable ot the sky, con- 
J verts it to a blue of various degrees ot inten- 
j sity; or at least that it shares with the trans- 
parent air in this effect. 
| The next stage is dew, or rather haze, for 
the latter term seems more appropriate to the 
’ appearance of dew while it is falling. Here the 
- drops have so far become collected as to form 
I an aggregate faintly defined in the air. To 
this succeed various delinite aggregates, 
under the general term cloud. Out of the 
1 latter are formed rain, snow, and hail, by 
which the product of evaporation is finally 
restored to the earth. The excess for any 
j given time, of the falling water over that which 
I is evaporated, passes olf by the springs and 
j rivers to that grand reservoir which forms the 
far greater part of the surface ot the globe. 
Tracts ot forest, especially if mountainous, 
; invite the rain, and protect the springs ; while 
the accumulated heat on cultivated plains 
| often causes the clouds to pass over them, or 
! to be dissipated. Clearing of land and cul- 
; ture, therefore, tend to lessen the rain and 
the rivers; but it is for the interest of agricul- 
i ture to leave a certain quantity of timber 
l growing, especially in springy lands, and to 
[ repair the waste of it by planting; for it is 
j not impossible, that in a series of ages, the 
axe and the plough too freely applied might 
convert a tract of fruitful country into one 
little better than an African desert. 
The mean annua! quantity of rain is greatest 
at the equator, and decreases gradually as we 
approach the poles. Thus at 
Granada, Antilles, 12° N. lat. it is 126 inches 
Cape Frangoh, 
St. 
46' - - 
Domingo 
19° 
120 
Calcutta - - 
- 22 
23 - - 
81 
Rome - - - 
- 41 
54 - • 
39 
England - - 
- 33 
.. - 
32 
Petersburgh - 
- 59 
16 - - 
16. 
On the contrary, the number of rainy days 
is smallest at the equator, and increases in 
proportion to the distance from it. From 
north latitude 12° to 43°, the mean number of 
rainy days is 78; from 43° to 46° the mean 
I number is 103; from 46° to 50° it is 134; 
f rom 5 1° to 60°, U> I . 
The number of rainy days is often greater 
in winter than in summer; but the quantity 
of rain is greater in summer than in winter. 
At Petersburg!! the number of rainy or snowy 
days during winter is 84, and the quantity 
which falls is only about live inches; during 
summer the number of rainy days is nearly 
| $he same, but the quantity which. falls is about 
f 1 inches. 
meteorology. 
More rain falls in mountainous countries 
than in plains. Among the Andes it is said 
to rain almost perpetually; while in Egypt it 
hardly ever rains at all. If a rain-gauge is 
placed on the ground, and another at somd 
height perpendicularly above it, more rain 
will be collected into the lower than into the 
higher; a proof that the quantity of rain in- 
creases as it descends, owing perhaps to the 
drops attracting vapour during their passage 
through the lower strata of the atmosphere 
where the greatest quantity resides. This, 
however, is not always the case, as Mr. Cop- 
land of Dumfries discovered in the course of 
his experiments. lie observed also, that 
when the quantity of rain collected into the 
lower gauge was greatest, the rain commonly 
continued for some time; and that the great- 
est quantity was collected in the higher gauge 
only either at the end of great rains, or dur- 
ing rains which did not last long. These ob- 
servations are important; and may, if fol- 
lowed out, give us new knowledge of the 
causes of rain. They seem to show, that 
during rain the atmosphere is somehow or 
other brought into a state which induces it to 
part with its moisture; and that the rain 
continues as long as this state continues. 
Were a sufficient number of observations 
made on this subject in different places, and 
was the atmosphere carefully analysed dur- 
ing dry weather, during rain, and immedi- 
ately after rain, we might soon perhaps dis- 
cover the true theory of rain. 
Rain falls in ail seasons of the year, at all 
times of the day, and during the night as well 
as the day ; though, according to M. Toaldo, 
a greater quantity falls during the day than 
the night. The cause of rain then, whatever 
it may be, must be something which operates 
at ail times and seasons. Rain falls also dur- 
ing the continuance of every wind, but often- 
est when the wind blows from the south. 
Falls of rain often happen likewise during 
perfect calms. 
It appears from a paper published by M. 
Cotte in the Journal de Physique for Oct. 
1791, containing the mean quantity of rain 
falling at 147 places situated between north 
lat. 11° and 60 °, deduced from tables kept at 
these places, that the mean annual quantity 
of rain falling in all these places is 34.7 inches. 
Let us suppose then (which cannot be very 
far from the truth) that the mean annual 
quantity of rain for the whole globe is thirty- 
four inches. The superficies of the globe 
consists of 170,981,012 square miles, or 
686,401,498,471,475,200, square inches. The 
quantity of rain therefore falling annuaUywiil 
amount to 23,337,650,8 12,030, 156,800 cubic 
inches, or somewhat more than 91,751 cubic 
miles of water. 
'Plie dry land amounts to 52,745,253 square 
miles; the quantity of rain falling on it annu- 
ally therefore will amount to 30,960 cubic 
miles. The quantity of water running annu- 
ally into the sea is 13,140 cubic miles; a 
quantity of water equal to which must be 
supplied by evaporation from tiie sea, other- 
wise the land would soon be completely 
drained of its moisture. 
The quantity of rain falling annually in 
Great Britain may be seen from the following 
table t which is probably the most extensive 
of the kind ; and as accurate as the use of in- 
struments, not constructed by one person 
and adjusted to a common standard, will al- 
17 * 
low. It is mostly compiled from the Transac- 
tions of different learned societies. 
Counties Mean ann. depth 
(maritime). Places. in inches. 
Cumberland. - Keswick, 7 years - 67. 5 
Carlisle, 1 year - 20. 2 
IV estmoreland. Kendal, 11 years - 59. 8 
Fell-foot, 3 years - 55. 7 
Waith Sutton, 5 years 46 
Lancashire. - Lancaster, 10 vears - 45 
Liverpool, 18 years - 34. 4 
Manchester, 9 years - 33 
Townley - - 41 
Crawshawbooth, near Has- 
li ogden, 2 years 
60 
Gloucestersf/i re. 
Bristol, 3 years 
29. 2 
Somersetshire'. 
Bridgewater, 3 years 
29. 3 
Cornwall. 
Ludguan, near Mount’s 
Bay, 5 years 
41 
Another place, 1 year 
29. 9- 
Devonshire. 
Plymouth, 2 years 
46. 5 
Hampshire. - 
Sel bourne, 9 years 
37. 2 
Fyfield, 7 years 
25. 9 
Kent, 
Dover, 5 years 
37. 5 
JEssex. 
Upminster - - 
19. 5 
Norfolk. 
Norwich, 13 years 
25. 5 
Yorkshire. 
Barrowby, near Leeds, 6 y 
27. 5 
Garsdale, near Sedbergh, 
3 years - - 52. 3 
Northumberland. Widdrington, 1 year — 21. 2 
Counties (inland). Places. Means. 
Middlesex. - London, 7 years - 23. 
Surry. - South Lambeth, 9 years- 22. 7 
Hertfordshire. Near Ware, 5 years - 25 
Huniingdonsb. Kimbolton, 7 years — 25 
Derbyshire. - Chatsworth, 15 years 27. 8 
Rutlandshire. Lyndon, 21 years 24. 3 
Northamptonsh. Near Oundle, 14 years 23 
General mean - 35.2 
As the places subject to much rain predo- 
minate considerably in this list, it will pro- 
bably be nearer the truth, if we take the 
mean annual rain in England and Wales at 
a quantity not exceeding 32 inches. 
In tliis country it generally rains less in 
March than in November, in the proportion 
at a medium of 7 to 12. It generally rains 
less in April than October in the proportion 
of 1 to 2 nearly at a medium. It generally 
rains less in May than September; the chances- 
that it does so are at least 4 to 3 : but when 
it rains plentifully .in May (as 1.8 inches or 
more), it generally rains but little in Sep- 
tember; and when it rains one inch or less in. 
May, it rains plentifully iu September. 
Snow is evidently formed by a process- of 
regular crystallisation among minute frozen, 
particles of water floating in the air. It h 
remarkable, that previous to, and during, trie 
fall of snow in quantity, the temperature con- 
tinues about 32°. It should seem, that the 
evolution of the constituent calorie of tiie 
water produces tiie same effect when ice is 
formed in the atmosphere, as when it is form- 
ed in water. The structure of a crystal of 
snow demonstrates that a drop of rain is also- 
formed by tiie union of a great number of 
smaller drops. When tiiese come together, 
in the act of freezing, and suddenly, they 
form a nucleus of white spongy ice, which,, 
by its extreme coldness, becoming incrusted, 
with clear ice from the water it collects in, 
its descent, constitutes hail as we usually see 
it. Sometimes, however, the nucleus falls 
unincrusted, which is a prognostic of sharp 
musts. Hail has been likewise observed per- 
fectly transparent, and having the form of 
an oblate spheroid, showing that it consisted 
, 1.0 . 
