METEOROLOGY. 
€d die lower term of congelation, which 
varies with circumstances and seasons, M. 
Boiiguer places another, called by him the 
upper term, and beyond this no visible 
vapour ascends. The former gentleman sup- 
poses this line far less liable to variation in 
the summer than the lower term, and there- 
fore adopted it to ascertain the rate of 
diminution of heat on ascending into the 
atmosphere. Bouguer determined the 
height of this term in one instance, but 
Kirwan went further, and produced a table 
of its height for every degree of latitude 
in the northern hemisphere. We shall 
quote Mr. Kirwau’s rule for obtaining the 
temperature at any given height, admitting 
that the temperature at the surface of the 
earth is known. “ Let the observed tem- 
perature at the surface of the earth be = 
m, the height given = ft, and the height of 
the upper term of congelation for the given 
. m — 32 , . 
latitude be = f ; then -r— — ■ =the dmn- 
— 1 
100 
nution of temperature for every 100 feet of 
elevation; or it is the common difference 
of the terms of the progression required. 
Let this common difiereuce thus found be 
denoted by c, then c x — gives us the 
whole diminution of' temperature from tire 
surface of the earth to the given height, 
Let this diminution be denoted by d, then 
m — d is obviously the temperature re- 
quired. An example will make this rule 
sufficiently obvious. In latitude 56°, the 
heat below being 54”, required the tem- 
perature of the air at the height, of 803 
feet. 
Herera=54,f=5,5j3, - 
' t 54.33 
h 
=z 0.404 =c,and c x 0.404 X 8.03= 
3 , 24 = d, and TO — = 54 — 3.24 =50.75 : here 
we see that the temperature of the air 803 
feet above the surface of die eartli is 50° 75 ". 
Estimating the diminution from this me- 
thod, which corresponds with observation, 
we find that heat lessens in an arithmetical 
progression ; and from the same premises it 
may be concluded, that the warmth of the 
air at some distance from the earth is not to 
be attributed to the rising of heated strata of 
air from the earth’s surface, but to the con- 
ducting power of the air. 
The upper strata of the atmosphere are 
frequently warmer in winter than the lower, 
and the preceding rule is applicable to the 
temperature of the air during the summer 
months only. According to the Philosophi- 
cal Transactions for 1777, a thermometer 
placed on the summit of Arthur’s Seat, the 
thirty-first of January, the year before, stood 
six degrees higher than a second at Hawk- 
hill, situated 684 feet below it: this superior 
heat is considered by Mr, Kirwan to be 
produced by a current of heated air flowing 
from the equator towards the north pole 
during our winter. A general idea has now 
been given of the method by which the 
mean annual temperature may be found 
throughout the known regions of the globe ; 
but there are some exceptions to the uni- 
versality of the rules ; for instance, the Pa- 
cific Ocean, between latitude 52° and 66° 
north, and at the northern extremity, is only 
42mile,«in breadth, and at its southern islSOO 
miles ; it is therefore but reasonable to sup- 
pose, that the temperature must be greatly 
affected by the land surrounding it, which 
rises into chains of mountains, with summits 
bearing snow great part of the year, exclu- 
sive of the islands consisting of high lands 
scattered within it. Mr. Kirwan concludes, 
in consequence, that its temperature is four 
or five degrees below the standard. This sup- 
position cannot, however, be brought to 
any degree of certainty, from a deficiency 
of observations. It has been a generally 
received opinion, that the southern hemis- 
phere, beyond the fortieth degree of lati- 
tude, is much colder than corresponding 
parts of the northern ; this our philosopher 
has proved to be true with respect to the 
summer of the former; but that the win- 
ter in the same latitude is milder than in the 
lattei'. 
Inconsiderable seas, in temperate and cold 
climates, aie colder in winter and warmer 
in summer than the standard ocean, as they 
are necessarily under the influence of natu- 
ral operations from the land, and its tempe- 
rature, particularly the Gulph of Bothnia, 
which is generally frozen in the winter, but 
the water is sometimes heated in the sum- 
mer to 70°, a state tlie opposite part of the 
Atlantic never acquires; the German Sea 
is five degrees wanner in summer than the 
Atlantic, and more than three colder in 
winter ; the Mediterranean is almost through- 
out warmer both in winter and summer, 
which therefore causes the Atlantic to flow 
into it ; and the Black Sea being colder 
than the Mediterranean, flows into the lat- 
ter. 
It appears from meteorological tables, 
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