250 
METEOROLOGY'. 
I. Of the Weather. 
The difficulty of forming a corredt theory of the wea¬ 
ther may eafily be conceived, when we confider that it is 
requifite for a perfon to have a large colledtion of fadts, 
and an extenlive acquaintance with feveral collateral fci- 
ences; for inftance, with mechanics, pneumatics, eledtri- 
city, and chemiftry. 
The principal inftruments of ufe in this branch of me¬ 
teorology are, the barometer, by which the weight or 
preflure of the atmofphere over any place is known ; the 
thermometer, which afcertains the temperature of the 
air; the hydrometer, to denote the moifture or drynefs 
of the air 5 the pluviameter, or rain-gauge, to meafure 
the depth of rain that falls 5 the evaporation-gauge, to 
fhow the depth of water evaporated 5 the anemofcope, to 
point out the diredtion of the wind ; the anemometer, to 
meafure its force ; and the eledtrometer, to afcertain the 
kind and intenfity of eledtricity in the air. See thofe 
words, and the articles Chemistry, Electricity, and 
Mechanics. 
In order to form a proper notion of the phenomena of 
the atmofphere, as exhibited at any one place, it will be 
neceflary to obtain a corredt notion of the atmofphere it- 
felf at large. It appears to be a colledtion or mixture of 
various elaftic fluids in very different proportions, retained 
on the furface of the earth by their gravitation. The 
principal part of the weight of the atmofphere arifes from 
the permanently elaftic fluids, azotic gas and oxygenous 
gas, the quantities of which are as 4 to 1 nearly : about 
one part in a thoufand of the atmofphere is conftituted of 
another permanently elaftic fluid, carbonic acid. The 
reft of the atmofphere confifts of aqueous vapour or fteam, 
an elaftic fluid fubjedt to partial condenfation by a dimi¬ 
nution of temperature. The quantity of this elaftic fluid 
is variable at different places and in different leafons 5 it 
may perhaps conftitute -^th of the weight of the whole 
atmofphere, confidered as a general average for the earth; 
but in fome places within the torrid zone it may amount 
to -jgth of the weight of the incumbent atmofphere ; and 
in the polar regions may fometimes be lefs than -5-3005dth 
part of the atmofphere. It is this portion of the atmo¬ 
fphere which more immediately occafions fome of the 
principal phenomena in meteorology, particularly clouds, 
min, hail, fnow, dew, and thunder and lightning : it has 
confiderable influence on the temperature of the atmo¬ 
fphere ; but it has little effedl in the produdtion of winds, 
or on the variation of the barometer. 
The atmofphere decreafes in denfity as we afcend in a 
geometrical progreflion to equal afcents. As far as expe¬ 
rience warrants the concluiion, the feveral kinds of gas 
decreafe in denfity in the fame ratio 5 thus, if at three 
miles in height the weight of the atmofphere is one-half 
what it is at the earth’s iurface, then will the proportions 
of the feveral elaftic fluids found in a given volume of 
air, at that place, be the fame as what they are in a like 
volume of air taken at the furface of the earth ; all the 
kinds being diminilhed one-half nearly in weight and 
denfity. This concluiion is not, perhaps, ftridtly true for 
every height, nor tor any two heights ; but experiments 
have not been made wdtli fuflicient accuracy to afcertain 
the deviation from this law. At fix miles elevation, the 
barometer w'ould ftand at the height at the furface, or 
at 7^ inches; at 9 miles of elevation, 3J inches; at 12 
miles, if inch; and at 15 miles, nearly 1 inch. Hence 
it teems that the greateft part of the atmofphere is at all 
times within 15 or 20 miles of the furface of the earth ; 
and it is probable that the ordinary phenomena of winds, 
clouds, rain, &c. are chiefly confined within much nar¬ 
rower limits, See the article Atmosphere, vol. ii. 
There is, however, one remarkable character of the 
atmofphere, namely, that of the uniform decreafe of 
temperature in afcending, which lias never been fatis- 
iadtorily explained. An ingenious eflay on this fubjedt 
has lately been publilhed, from which we fliall here give 
fome extradls. 
“ It is a remarkable faff, and has never, I believe, been 
fatisfadlorily accounted for, that the atmofphere in all 
places and leafons is found to decreafe in temperature in 
proportion as we afcend, and nearly in an arithmetical 
progreflion; that is to fay, the nearer we go to the fun, 
the colder we are ! Sometimes the fadl may have been 
otherwife, namely, that the air was colder at the furface 
of the earth than above, particularly at the breaking of 
a froft I have obferved it fo ; but this is evidently the 
eftedt of great and extraordinary commotion in the at¬ 
mofphere, and is at moft of a very fliort duration. What 
then is the occafion of this diminution of temperature in 
afcending ? Before this queftion can be folved, it may 
be proper to confider the defedts of the common folution. 
Air, it is faid, is not heated by the diredt rays of the fun, 
which pafs through it as a tranfparent medium, without 
producing any calorific effedt, till they arrive at the fur¬ 
face of the earth. The earth, being heated, communicates 
a portion to the contiguous atmofphere, whilft the lupe- 
rior ftrata, in proportion as they are more remote, receive 
lefs heat, forming a gradation of temperature, fimilar to 
what takes place along a bar of iron when one of its ends 
is heated. 
“ The firft part of the above folution is probably cor¬ 
redt : air, it fliould feem, is Angular in regard to heat; it 
neither receives nor difcharges it in a radiant ftate ; if fo, 
the propagation of heat through air muft be eftedted by 
its conducting power, the lame as in water. Now we know 
that heat applied to the under furface of a column of water 
is propagated upwards with great celerity, by the adtual 
afcent of the heated particles : it is equally certain, too, 
that heated air afcends. From thefe oblervations it fliould 
follow, that the caules afligned above for the gradual 
change of temperature in a perpendicular column of the 
atmoiphere, would apply diredtly to a ftate of tempera¬ 
ture the very reverfe of the fadf ; namely, to one in which 
the higher the afcent, or the more remote from the earth, 
the higher fhould be the temperature. 
“ Whether this reafoning be corredt or not, it muft, I 
think, be univerfally allowed, that the fadt has not hi¬ 
therto received latisfadtory explanation. I conceive it to 
be one involving a new principle of heat; by which I 
mean a principle that no other phenomenon of nature 
prefents us with, and which is not at prefent recognifed 
as fuch. I fliall endeavour in what follows to make out 
this pofition. 
“ The principle is this : The natural equilibrium of 
heat in an atmofphere , is when each atom of air in the fame 
perpendicular column is pojfeffed of the fame quantity of heat.; 
and, confequently, the natural equilibrium of heat in an at¬ 
mofphere is when the temperature gradually diminijhcs in qf- 
cending. That this is a juft conlequence cannot be de¬ 
nied, when we confider that air increafes in its capacity 
for heat by rarefadtion ; when the quantity of heat is 
given or limited, therefore, the temperature muft be re¬ 
gulated by the denfity. It is an eftabliftied principle, 
that any body on the furface of the earth unequally 
heated is obferved to tend conftantly towards an equality 
of temperature ; the new principle announced above, 
teems to liiggeft an exception to this law. But it it be 
examined, it can fcarcely appear in that light. Equality 
of heat and equality of temperature, when applied to the 
lame body in the lame ftate, are found fo uniformly to be 
aflbciated together, that we lcarcely think of making any 
diftindtion between the two expreflions. No one would 
objedt to the commonly-obferved law being exprefied in 
thefe terms : When any body is unequally heated , the equi¬ 
librium is found to be rejlored when each particle oftlLe body 
becomes in pojj'cjjion of the fame quantity of heat. Now the 
law thus exprelfed is what I apprehend to be the true ge 
neral law, which applies to the atmoiphere as well as to 
other 
