METEOROLOGY. 
Hpon strong probabilities supported iu many 
instances by positive experiment. 
It is singular that this science should have 
remained for so long a period in a state of 
comparative neglect, when it is recollected 
that almost all the operations necessary for 
the support of human life, and almost all the 
comforts of corporeal feeling, depend upon 
the state of the atmosphere, and yet nothing 
was attempted to any purpose towards in- 
vestigating the laws of meteorology till the 
seventeenth century, when the most im- 
portant discoveries of the barometer and 
thermometer occurred, which was followed 
in the eighteenth by the invention of ex- 
cellent hygrometers and electrometers ; by 
these the philosopher finds himself com- 
petent to make accurate and satisfactory 
observations. Scientific persons, who have 
particularly turned their attention to this 
pursuit, have undertaken the laborious task 
of collecting and methodically arranging 
numbers of the observations just mentioned, 
and after attentively comparing and exa- 
mining them have formed theories of the 
weather of more or less probable accuracy ; 
but the science is of such difficulty that 
though those theories deserve every praise, 
we are compelled to acknowledge the pheno- 
mena of the weather is still very imperfectly 
understood. This acknowledgment, how- 
ever, reflects no discredit on those ingeni- 
ous men, as it is impossible that any thing 
like certainty should be attained, till ob- 
servations that can be depended upon are 
procured from all parts of the globe, the 
atmosphere has been more accurately ex- 
plored, and the chemical changes occurring 
in it are correctly ascertained. 
To render our explanation of this subject 
as satisfactory as circumstances will permit 
we shall proceed in the succession before 
pointed out; with respect to the changes 
in the weight of the atmosphere, it is gene- 
rally known that the instrument called the 
barometer shews tlie weight of a body of 
air immediately above it extending to the 
extreme boundary of the atmosphere, and 
the base of which is equal to that of the 
mercury contained within it. As the level 
of the sea is the lowest point of observation, 
the column of air over a barometer placed 
at that level is the longest to be obtained ; 
in this case the mean height of the baro- 
meter is thirty inches. According to the 
experiments of Sir George Sluickl)urgh in 
the Channel and tlie Mediterranean Sea in 
the temperature of 55 ° and 60", this was 
found to be the case, and the result is con- 
firmed by those of M. Bouguer on the 
coast of Pern in the temperature of 84", 
and I.ord Miilgrave in latitude 80". From 
these data, it is evident that the mean 
height of the barometer decreases in pro- 
portion with its elevation above the level 
of the sea, and in proportion to the conse- 
quent shortening of the columns of air ; 
hence it is used for measuring heights. The 
keeping of a barometer in one particular 
place does not make the mercury stationary, 
as it will vary by rising or falling to the 
extent of several inches, of necessity the 
weight of the air which balances the mer- 
cury must be subject to the same changes ; 
this circumstance proves that the gravity of 
the air in any given situation varies greatly, 
being at one time light and another heavy, 
an effect which must be caused by changes 
in its quantity, and a fact that demonstrates 
the air of every place liable to perpetual 
alterations, which must arise from the accu- 
mulation of air in particular places, and a 
reduction in others, “ or,” as Dr. Thomson 
observes, “ part of the atmosphere must 
be alternately abstracted altogether, and 
restored again by some constant, tliough 
apparently irregular process.’’ 
Tlie variations of the barometer between 
the tropics are very trifling, and it is worthy 
of observation, it does not descend more 
than half as much in that part of the globe 
for every two-hundred feet of elevation as 
it does beyond the tropics, which we learn 
from the Journal de Physique ; besides, the 
barometer rises about two-thirds of a line 
twice during each day in the torrid zone. 
We are informed by M. Horsbiirgh that 
from latitude 26° north to latitude 27* 
south, which includes the space termed 
tlie tropical seas, the mercury attained its 
greatest elevation at eight in the morning, 
from which hour till noon it continued 
stationary, it then began to fall and descend- 
ed till about four o’clock, when it reached 
the lowest point of depression. In the in- 
terval between four and five the mercury 
rose, and continued to rise till about nine 
or ten P. M. when it had once more ar- 
rived at its most elevated point, where it 
remained stationary till near midnight, 
when it fell and continued , to fall, till at 
four A. M. it had descended as low as it 
had been at four in the afternoon; from 
that period till seven or eight it continued 
rising, and at the latter hour it had attained 
the highest point’of elevation. The gentle- 
