768 C G 
tor, and, were we to form our judgment from its fituatiom 
on the globe, we (hould fuppoJe it oppreffed with intoler¬ 
able heat; the air, however, is abundantly temperate, 
and differs very little from that of Paris. Quito is fituated 
at a great height above the real furface of the earth. In 
going to it from the lea Ihore, we,have to afcend for feve- 
ral days; it is accordingly built in an elevation equal to 
that of our highelt mountains, though furrounded by 
others Hill much higher, called the Cordeliers. This lalt 
circumftance would afford a reafon for thinking, that the 
air there muff be as hot as at the furface of the earth, as it 
is contiguous, on all fides, to opaque bodies, on which the 
rays of the fun fall. The objection is foiid ; and no folu- 
tion can be given but this : that the air at Quito, being 
very elevated, muff be much more fubtile, and of lels 
gravity, than with us; and the barometer, which always 
ltands coniiderably lower, inconteftably proves It. Air 
of filch a quality is not fo fufceptible of heat as common 
air, as it muft-contain lefs vapour and other particles 
which ufually float in the atmofphere; and we know by 
experience, that air, very much loaded, is proportionably 
fufceptible of heat. I muff here fubjoin another pheno¬ 
menon, no lefs furprifing.: in very deep pits, and lower 
ftill, if it were ftdl poflible to defcend, the fame degree 
of heat always, and univerfaily, prevails, and nearly for 
the fame reafon. As the rays of the fun exert their in¬ 
fluence only on the furface of the earth, and as the heat 
which they there excite communicates itfelf up and 
down, this effect, at very great depths, is almoft imper¬ 
ceptible. The fame thing holds refpefting confiderable 
heights.” 
The reafon which Profeffor Euler affigns above for the 
cold that prevails in the higher regions of the atmofphere 
leems plaufible, but will not ftand an accurate.examina¬ 
tion. Light is much impaired in its paflage through the 
atmofphere, and the heat communicated is in every cafe 
proportional to the quantity of abforption. It appears, 
from fome ingenious experiments of M. Bouguer, that 
we receive only four fifths of the rays of a vertical fun ; 
and when that luminary approaches the horizon, the por¬ 
tion of his light, which reaches the furface of the earth, is 
much fmaller. Thus, at an elevation of twenty degrees, 
it is one-half; at that of ten degrees, one-third; and at 
that of five degrees, one-eighth. Hence, the fun-beams 
are moft powerful on the iummits of lofty mountains, 
for they fuffer the greateft diminution in palling through 
the denfe air of the low'er regions. If the air derived its 
heat from the furface of the earth, thofe countries wouid 
lie warmeft which enjoyed the greateff quantity of fun- 
lhine. The Britifti illands are (hrouded in clouds nine 
months of the year ; yet our climate is milder than that 
of the fame parallel on the continent, where the Iky is 
generally lerene. The elevated town of Quito, expofed 
to a brilliant fun, enjoys a temperate air ; while the Peru¬ 
vian plains, (haded with fleecy clouds, are parched with 
heat. Were the reafoning above to be implicitly admit¬ 
ted, weffiould conclude, that the tops of mountains are 
warmer than their bafes. To fay that air, much rarefied, 
is not fufceptible of heat, is a very extraordinary afler- 
tion, flnce we are acquainted with no fubftance whatever 
that may not be heated. Befides, a more intenfe cold 
may be artificially produced than what prevails in the 
lofty regions of the atmofphere. We muff recur to other 
principles for the true (olution of the fail. It is indifferent 
what portion of the air firft receives the heat; the effeft de¬ 
pends entirely on the nature of its diftribution. If the 
atmofphere were of an uniform denfity throughout, the 
heat would, at all heights, be v likewife the fame. But as 
the denfity .varies according to the altitude, the diftribu¬ 
tion of heat is afteCled by that circumftance, and follows 
a certain correfponding law. We would gladly develope 
the principles from which this theory is deduced, but 
'the popular nature of the prefent trentife forbids all ab- 
ftraCt dilcuflion. It will here be fufficient to give a table 
vf the diminuition of heat at different altitudes* 
D. 
Altitude in feet. 
Diminution of heat, in degrees 
of.Farenheit. 
3 ,°°o 
—■ 
— — 12° 
6,000 
— 
’ 1 ^ 4 j 
9,000 
— 
- — 38 
12,000 
— 
— — 53 
3 5,000 
— 
— — 681 - 
18,000 
— 
— — 861 
21,000 
— 
1 
1 
VO 
The diminution of heat, oil the afcent, is not quite fo 
great in extenfive continents ; for the intercourfe between 
the rare and the denfe portions of the atmofphere is, in 
this cafe, neceflarily flow, and the heat, which is princi¬ 
pally formed at the furface, will only be partially dif- 
perfed. It is a common raiftake to fuppofe,.tiiat the fame 
heat obtains, at a certain depth, in every part of the 
globe. The fadt is, that heat, originally derived from 
the fun, is communicated .very (lowly to the matter be¬ 
low the furface, which, therefore, does not feel the vicif- 
fitude of feaions, but retains the average temperature of 
the climate for many ages. Hence the utility of examin¬ 
ing the heat of fprings, which is the fame with that of 
the fubftances through which they flow. The following 
table exhibits the average heat of places on the level of 
the lea, computed by the celebrated aftronomer, Prolel- 
lor Meyer, (or every five degrees of latitude. 
Lat. 
Average Temperat. 
Lat. 
Average Temperat 
0 
— — 84° 
50 
- 53 |° 
c 
- 
55 
— — 49 
10 
— — 824 
60 
— — 45 
15 
—• — 8oi 
65 
— ~ 44 
20 
— — 78" 
70 
— - 38 
25 
— — 74 a- 
75 
— — 35 | 
3 ° 
- - 71 
80 
— — lii 
35 
— — 67 
85 
- 34 
40 
45 
- 64 
-58 
90 
By comparing this table with the preceding, it will 
be eafy to difcover, for any latitude, the altitude of the 
curve of congelation, or where the average tempera¬ 
ture is 32 0 . With refpeft to the influence of cold 
upon the health of man, a very interefting enquiry 
has been lately made by Dr. W. Heberden, with a view 
to afeertain its etfedfs upon the inhabitants of the 
city of London. The winter of 1795 and that of 1706, 
were extraordinarily contraffed ; the firft being one of 
the coldeft, the laft one of the warmeft, on record. During 
January 1796, nothing was more common than to hear 
expreflions of the unfealonablenefs of the weather; and 
fears left the want of the ufual degree of cold (hould be 
productive of putrid difeales, and other caufes-of mor¬ 
tality. On the other hand, “ a bracing cold,” and “ a 
clear froft,” are familiar in the mouth of every Englifli- 
maa; and what he is taught to wi(h for, as among the 
greateft promoters of health and vigour. Whatever de¬ 
ference be due to received opinions, it appears, however, 
from the (trongeft evidence, that the prejudices of the 
world are upon this point ac lealt unfounded. The 
average degrees of heat upon Fare.nheit’s thermometer 
kept in London during the month of January 1795, was 
23° in the morning, and 29-4 degrees in the afternoon. 
The average in January 1796, was 43-5 degrees in the 
morning, and 50'x degrees in the afternoon. A difference 
of above twenty degrees! And if we turn our attention 
from the comparative coldnels of thefe months, to the 
correfponding healtbinefs of each, collected from the 
weakly bills of mortality, we (hall find the refult no lefs 
remarkable. For in five weeks, between the 31ft of De¬ 
cember 1794, and the 3d of February 1795, the whole 
number of burials amounted to 2823 ; and in an equal 
period of five weeks between the 30th of December 1795, 
and the 2d of February 1796, to 1471 ; fo that the excefs 
of the mortality in January 1795 above that of January 
1756* 
