62 
ene fquare foot is equal to rather more 
than 83lb. avoirdupoife = 15°76 inches 
im depth, which is nearly the mean quan- 
tity of rain that falls in the metropolis in 
the drieft years. (2) That evaporation ts 
nearly the fame in winter as in Summer. 
(3) That rain does not prevent evapora- 
tion. (4) That the cold produced is pro- 
o:tioned to the quantity of evaporation. 
The Second Chapter treats of the fiate 
of vapour in the atmofphere. 
That vapour may fabfft in highly rare- 
fied air, is known from the obfervations 
of Rouguer, who faw clouds fo far above 
Chimborago, as to be at leaft 4.3 miles 
above the ievel of the fea, where the baro- 
meter would at a temperature of 32° ttand 
at 12.7 inches. It is known aldo, that 
water which boils at 2129 when the baro- 
meter fiancs at 30 inches, will, as the 
preflure diminifhes, boil at a much lower 
heat, according to the following table. 
HEAT OF BUILING WATER. 
bar. | Heat. Bar. | Heat. 
30 | 2120 21 |'195.36° 
29 2.10.28 20 193-3 
28 208.52 19 191.06 
27 206.73 13 188.46 
26 204:91° 17 185.56 
25 2.03.06 16 184.36 
2A. 201.18 |; 15 180.386 
Ze 199.77 |} 34 176.70 
22 707.3% 
Hence diftillation may be more advan- 
tageoufly effected on mountains than on 
plains; yet within certain limits, for at 
heights that furpa‘s 8 or ro thoufand feet, 
fuel is copfumed very flowly. 
From other obfervations and tables, it 
is deduced, that air faturated with moif- 
ture at high heats, is much more expanded 
than dry air of the fame temperature; that 
moift air; fuch as that of the Weft Indies, 
is much more ‘{vffocating than dry air of 
the fame temperature. 
Chap. III. treats of the temperature of 
the atmolphere, and contains the invefti- 
gation of feveral curious problems, with 
regard to the degrees of heat, at different 
heights above the earth’s furface, and me- 
thods of calculating them from’ certain 
data. From which, among other fubjefis, 
it is inferred, that the difference be:ween 
the temperature of mountains and of 
plains, is not fo great in winter as in 
fummer ; that in winter the temperature 
at great heights is often warmer than on 
lains; confequently, that thermometers 
placed at different heights will give diffe- 
rent refults. Ei has been found, that about 
Proceedings of Learned Societies. 
[Aug. 1, 
eleven o'clock in the forenoon, in winter, 
the temperature on the fummits of 
high mountains, is exa¢tly the fame as 
that of plains; a circumftance that never 
occurs in fummer. Thaws generally be- 
gin above, and are pradually propagated 
downwards. The North Pacific Ocean, 
above lats 40°, is much colder than the 
North Atlantic betwixt the fame parallels. 
The interior parts of Siberia, eaft of lon- 
gitude roo°, are much colder than parts 
equally diftant from that meridian on the 
wettern Gide. The coaft and interior of the 
weltern regions of America, are much 
colder above lat. 409, than the correfpond- 
ing tracts of the European continent.— 
Barometers, in the northern parts of Eu- 
rope, at lea(t, generally ftand highet in 
the months of December, January, and 
February. Both the higheft and lowett 
ftates of the barometer eccur in the winter 
months. It is alfo well known, that the 
fmalleft variations occur within the tro- 
pics, but gradually increafe as we recede 
from them. “The remainder of this chap- 
ter treats of the origin of the general 
trade-winds—of variable winds from all 
the quarters—of oppofite concomitant 
winds—of the fucceffion of winds—of the 
firocco, the malignity of which is imputed 
to the fmali quantity of oxygen that it 
contains; while the harmattam, though 
injurious, in fome refpects, to the confti- 
tution, deftroys infection, and cures feve- 
ral diforders. It treats alfo of the varia- 
tions of the temperature of the fummer 
and winter feafons in different years—of 
the temperature of the fouthern hemi- 
fphere. 
In the Fourth Chapter, entitled “* Of the 
Denfity of the Atmofphere,” there 1s a 
confiderable body of elementary inftruc- 
tion. It contains a valt number of pro- 
blems, with their feveral folutions ; the 
application of the barometer to the mea- 
furing of heights, with the proper methods 
for detecting errors on this fubject; and 
other important topics, illuftrated with fe- 
veral tables. 
The Fifth Chapter, «© On the Precipita- 
tions of the Atmofphere ;”” after deferib- 
ing the five principal fubftances contained 
in the lower ftrata of the atmofphere, with 
which we are principally concerned, viz. 
oxygen, mephite, moifture, caloric, and 
the electric fluid, is divided into four 
fe€tions. The firf relates to atmofpherie 
electricity ; and from certain oblervations 
and principles Jaid down, Mr. Kirwan de- 
duces, (1) That the vapours emitted in 
different latitudes, and at different feafons 
of the year, contain different portions of 
electric 
