m 
Here m — 54, t 
„„„ ™ ~ S2 22 
55 33, — — - . 
t _ 54.33 
100 
— °- 401 = c > anti e X = 0.404 x 8.03 — 
100 
3.34 " and tx — d ~ 54 — 3.34 — 50.75. 
Here we see that the temperature of the air 803 
feet above tiie surface of the earth is 50°. 75. 
I'rom this method of estimating the dimi- 
nution of temperature, which agrees remark- 
ably well with observation, we see that tin* 
heat diminishes in an arithmetical progres- 
sion. Hence ;t follows, that the heat of the 
air at a distance from the earth is not ow- 
ing to the ascent of hot strata of air from the 
surface of the earth, but to the conducting 
power of the air. 
a. I his rule, however, applies only to the 
temperature of the air during the summer 
months of the year. In winter the upper 
strata of the atmosphere are often warmer 
tiian the lower. Thus, on the 3 1st of Janu- 
ary, 1 77b, the thermometer on the summit 
of Ai thui s-seat stood six degrees higher than 
a thermometer at Hawklnll, which is (>84 
ieet lower. Mr. Kirwan considers this su- 
perior heat, almost uniformly obs rved dur- 
ing winter, as owing to a current of warm. air 
from the’ equator, which roils towards the 
north pole during our winter. 
4 Such, then, in general is the method of 
finding the mean annual temperature over 
the globe. There are, however, several ex- 
ceptions to these general rules, which come 
now to be mentioned. 
1 hat part of the Pacific Ocean which lies 
_ between north latitudes 52° and 06°, is no 
’ broader at its northern extremity than 42 
miles, and at its southern extremity than 
1300 miles: it is reasonable to suppose, 
therefore, that its temperature will be con- 
siderably influenced by the surrounding 
land, which consists of ranges of mountains 
covered a great part of the year with snow; 
and there are besides a great many high, and 
consequently cold, islands scattered through 
it. For these reasons Mr. Kirwan concludes, 
tout its temperature is at least four or five 
degrees below the standard. Rut we are 
not yet furnished with a sufficient number of 
observations to determine this with accu- 
racy. 
If is the general opinion, that the southern 
hemisphere, beyond the 40th degree of lati- 
tude, is considerably colder than the corre- 
sponding parts of the northern hemisphere. 
Mr. Kirwan has shewn that this holds with 
respect to the summer of the southern hemi- 
sphere, but that the winter in the same lati- 
tudes is milder than in the northern hemi- 
sphere. 
Small seas surrounded with land, at least 
in temperate and cold climates, arc generally 
warmer in summer and colder in winter than 
the standai d ocean, because they are a good 
deal influenced by the temperature of the 
land. The gulf of Bothnia, for instance, is 
for the most part frozen in winter ; but in 
summer it is sometimes heated to 70°, a de- 
gree or heat never to be found in the oppo- 
site part of the Atlantic. The German Sea 
is above three degrees colder in winter, and 
five degrees warmer in summer, than the At- 
lantic. The Mediterranean Sea is, for the 
greater part of its extent, warmer both in 
summer and winter than the Atlantic, which 
METEOROLOGY. 
therefore flows into it. The Black Sea is 
colder than the Mediterranean, and flows 
into it. 
The eastern parts of North America are 
much colder t’nan the opposite coast of Eu- 
rope, and fall short of the standard by about 
10“ or 12°, as appears from American mete- 
orological tables. The causes of this remark- 
able difference are many. The highest part 
of North America lies between the 40th and 
50th degree of north latitude, and the 100th 
and 1 10th degree of longitude west from Lon- 
don; tor there the greatest rivers originate. 
The very height, therefore, makes this spot 
colder than it otherwise would be. it is co- 
vered with immense foreAs, and abounds with 
large swamps and morasses, which render it in- 
capable of receiving any great degree of heat ; 
so that the rigour of winter is much less tem- 
pered by the heat of the earth than in the 
old continent, I o the east lie a number of 
very large lakes; and farther north, Hud- 
son’s-bay ; about 50 miles on the south of 
which there is a range of mountains, which 
prevent its receiving any heat from that quar- 
ter. This bay is bounded on the east by the 
mountainous country of Labrador, and' by a 
number of islands. ' Hence the coldness' of 
the north-west winds, and the lowness of the 
temperature. But as the cultivated parts of 
North America are now much wanner than 
formerly, there is reason to expect that the 
climate will become still milder when the 
country is better cleared of woods, though 
perhaps it will never equal the temperature 
of the old continent. 
Islands are warmer than continents in the 
same degree of latitude; and countries h ing 
to the windward of extensive mountains or 
forests are warmer than those lying to the 
leeward. Stones or sand have a less capa- 
city tor heat than earth has, which is always 
somewhat moist; they heat or cool, therefore, 
more rapidly and to a greater degree. Hence 
the violent heat of Arabia and Africa, and 
the intense cold of Terra del Fuego. Living 
vegetables alter their temperature very slow- 
ly, but their evaporation is great ; and'if they 
are tall and close, as in forests, they exclude 
the sun’s rays from the earth, and shelter the 
whiter snow from the wind and the sun. 
Woody countries, therefore, are much colder 
than those which are cultivated. 
Air is one of those bodies which have re- 
ceived the name of electric, because they are 
capable of being positively or negatively 
charged with electric natter. It not only 
contains that portion of dec tricity which 
seems necessary to the constitution of all 
terrestrial bodies, but it is liable also to be 
charged negatively or positively when elec- 
tricity is abstracted or introduced by means 
of conducting bodies. These different states 
must occasion a variety of phenomena, and 
in all probability contribute very consider- 
ably to the various combinations and decom- 
positions which are continually going on in 
air. The electrical state of the atmosphere, 
then, is a point of considerable importance, 
and has with great propriety occupied the 
attention of philosophers ever since Dr. 
franklin demonstrated that thunder is occa- 
sioned by the agency of electricity. 
E The most complete set of observations 
on the electricity of the atmosphere were 
made by professor Beccaria of Turin, lie 
found the air almost always positively elec- 
| triea!, especially in the day-time and in dry 
| weather. When dark or wet weather clears 
| up, the electricity is always negative. Low 
! togs rising into dry air carry up a <>reat 
deal of electric matter. 
2. In the morning, when the hygrometer 
indicates dryness equai to that of the preced- 
ing day, positive electricity obtains even be- 
fore sunrise. As the sun gets up, this elec- 
tricity increases more remarkably if the dry- 
ness increases, it diminishes in the evening. 
3 The mid-day electricity of days equally 
dry is proportional to the heat. 
4. Winds always lessen the electricity of 
a clear day, especially if damp. 
5. for the most part, when there is a clear 
sky with little wind, a considerable electricity 
arises after sunset at dew-falling. 
6. Considerable light lias been thrown 
upon the sources of atmospherical electricity 
by the experiments of Saussure ap'd other 
philosophers. Air is not only electrified bv 
friction, like other electric bodies, but the 
state o; its electricity is changed by various 
cnemicai operations w hich often go on in the 
atmosphere. Evaporation seems in all eases 
to convey elect) c matter into the atmo- 
sphere. On the other hand, when steam is 
condensed into water, the air beo^jmes nega- 
tively electric. 
Farther, Mr. Canton has ascertained that 
dry air, when heated, becomes negatively 
electric, and positive when cooled, even 
when it is not permitted to expand or con- 
tract: and tiie expansion and contraction of 
air also occasion changes in its electric state. 
I hus there are four sources of atmospheric 
electricity known : 1. Friction; 2. Evapora- 
tion ; 3. Heat and cold; 4. Expansion and 
contraction : not to mention the electricity 
evolved by the melting, freezing, solution, 
&c. of various bodies in contact with air. 
7. As air is ail electric, the matter of elec- 
tricity, when accumulated in any particular 
strata, will not immediately make its way to 
the neighbouring strata, but will induce in 
them changes similar to what is induced upon 
plates of glass or similar bodies piled upon 
each other. Therefore, if a stratum of air is 
electrified positively, the stratum immediate- 
ly above it will be negative, the stratum 
above that positive, and so on. Suppose 
now that an imperfect conductor w'as to 
come into contact with each of these strata: 
we know from the principles of electricity 
that the equilibrium would be restored, and 
that this would be attended with a loud noise 
and with a flash of light. Clouds are imper- 
fect conductors . it a cloud, therefore, comes 
into contact with two such strata, a thunder- 
clap will follow'. If a positive stratum is 
situated near the earth, the intervention of a 
cloud will, by serving as a stepping-stone, 
bring th e stratum within the striking distance’ 
and a thunderclap will be heard while the 
electrical fluid is discharging itself into the 
earth. If the stratum is negative, the con- 
trary effects will take place, "it does not ap- 
pear, however, that thunder is often occa- 
sioned by a discharge of electric matter from 
the earth into the atmosphere. The acci- 
dents, most of them at least, w hich were for- 
merly ascribed to this cause, are now much 
more satisfactorily accounted for by lord 
stanhope’s theory of the returning stroke. 
1 he discharge from the clouds directly into 
