METEOROLOGY. 
1'70 
much slower. At Falkirk it began to snow 
at six in the evening of the 7th; at Edin- 
burgh, about one o’clock in the morning of 
the 8th; and at Dunbar, at eight o’clock in 
the morning. It lasted i 1 hours, and did not 
travel above 100 miles during that time. 
The north-east wind blows most frequently 
with us during the spring months ; and from 
the observations made by captain Cook, it 
appears, that the same wind prevails during 
the same period in tire northern Paciiic. 
Hence it appears, that at that season the cold 
air from the north of Europe and America 
Rows into the Atlantic and Paciiic. Hence 
the reason of its uncommon coldness, dry- 
ness, and density. 
it is very common td observe one current 
of air blowing at the surface of the earth, 
while a current flows in a contrary direction 
in the higher strata of the atmosphere. 
Three such winds have been observed blow- 
ing in contrary directions all at the same 
time. It is affirmed that changes of weather 
generally begin in the upper strata of the air, 
the wind which blows there gradually extend- 
ing itself to the surface of the earth." 
With regard to the pressure of the atmo- 
sphere, it is every where variable, as appears 
by the barometer ; which indicates to 11 s the 
weight of a column of air, extending to the 
top ot the atmosphere, and whose base is 
equal to that of the mercury. At the level j 
of the sea, where the column of air is longest, I 
the mean height of the barometer is thirty 1 
inches. This sir George Shuckburgh found to 
be the case in the Mediterranean and the 
Channel, in the temperature of 55° and 60°; 
Mr. Bouguer, on the coast of Peru, in the 
temperature of 84°; and lord Mulgrave, in 
latitude 80°. The mean height of the baro- 
meter is less, the higher any place is situated 
above the level of the sea, because the co- 
lumn of air which supports , the mercury is 
the shorter. 
Between the tropics the variations of the 
barometer are exceeding!)? small ; and it is 
remarkable, that in that part of the world it 
does not descend above half as much for 
every 200 feet of elevation as it does beyond 
the tropics. 
As the latitude advances towards the poles, 
the range of the barometer gradually in- 
creases, till at last it amounts to two or three 
inches. This gradual increase will appear 
from the following table: 
TABLE 
Of the Range of the Barometer. 
Range of the Ba- 
Latitude. 
Places. 
rometer. 
Greatest. 
Annual. 
0° 
O' 
Peru 
0.20 

22 
23 
Calcutta 
0 77 
— 
S3 
55 
Cape Town 
— 
0.89 
40- 
55 
Naples 
1. 00 
— 
51 
8 
Dover 
2.47 
1.80 
53 
23 
Liverpool 
2.89 
1.96 
59 
56 
Petersburgh 
3.45 
2.77 
In North America, however, the range of 
the barometer is a great deal less than in the 
corresponding European latitudes. In Vir- 
ginia, for instance, it never exceeds 1.1. 
The range of the barometer is greater at 
the level of the sea than on the 'mountains ; 
and in the same degree of latitude, the extent • 
of the range is in the inverse ratio of the 
height of the place above the level of the sea. 
f rom a table published by Mr. Cotte, in 
the Journal de Physique, it seems exceeding- 
ly probable that the barometer lias always a 
tendency to rise from the morning to the 
evening; and that this tendency is greatest 
between two o’clock in the afternoon and 
nine at night, at which hour the greatest ele- 
The range of the barometer is greater in 
winter than in summer. Thus at York the 
mean range of the barometer, during Octo- 
ber, November, December, January, Febru- 
ary, March, of the year 1774, was 1.42, and 
for the six summer months, 1.0 16. 
It is probable that the variations of the 
barometer, as well as those of the thermo- 
meter, are susceptible of what we may term 
a local character for each tractor country dif- 
fering in climate. This will be most readily 
discovered by the following mode of inves- 
tigation : Prepare a sheet of paper ruled in 
squares with pale ink; the horizontal lines 
agreeing with 'the inches and decimal divi- 
sions of the scale of the barometer ; the per- 
pendicular, which may be about twice as 
distant, representing divisions of time. ' It 
will be convenient to consider each line as 
denoting midnight, and to mark the days of 
the month at the top of the columns thus de- 
fined. On this scale let the several notations 
of any register of the barometer be set down 
by means of a dot for each, placed in the 
part of the scale where it may point out the 
time and the elevation. The desired num- 
ber of notations thus made, a curve may be 
drawn through the series of dots, which will 
represent at one view the course of the baro- 
meter for the time. It will be found, on 
comparing a number of these curves, that 
they characterize, in a certain degree, not 
only the latitude and season, but the locality 
of the observations. So that although the 
most obvious resemblances may be traced in 
different years of the same register, yet the 
general appearance of registers from differ- 
ent climates, will be found to differ in tfli 
respects. In this way may be seen at one 
view both the correspondence between the 
latitude or elevation above the sea of any 
place, and the range at that place ; and the 
coincidence between the movements of the 
j vatlon takes place ; that the elevation of nine 
! o’clock differs from that jaf two by A-ths, 
while that at two differs from the morniag 
elevation only by and that in certain 
climates the greatest elevation takes place at 
two o’clock. The following is a part of the 
table on which these observations are founded, 
reduced to the English standard. 
barometer, and the other phenomena of the 
weather. It is obvious that the same mode, 
and even tire same scale, may be made to 
serve for temperature also, by marking de- 
grees upon tne horizontal lines, ai-tcl changing 
the appearance of the line representing tem- 
perature, so as to make it readily distinguish- 
able from the other curve. There is a cor- 
respondence in this climate between the two 
instruments, which will thus often become 
conspicuous. It consists in an elevation of 
temperature after a rise of the barometer, 
and vice versa: tl>e exceptions to this occur 
chiefly at the setting.in ot frost, and when it 
rains with the wind from the eastward. But 
the most remarkable circumstance w hich has 
been thus brought to light is, an influence 
which the sun and moon exercise over the 
atmosphere in respect to its pressure; and 
which is detailed in a series of observations, 
accompanied with a chart of this kind, for 
the year 1798, in the Philosophical Maga- 
zine, vol. vii. p. 355. 
r l he elfect of this is, a tendency in the at- 
mosphere to gain weight while the moon is 
passing to either quarter, and vine versa to 
lose it during the approach of full or new 
moon. The actual change which on a mean 
of ten years is found always to take place at 
London, amounts only to two-tenths ef an 
inch in the barometer, which thus occurs 
twice in each moon. The apparent influ- 
ence is often much greater tor a considerable 
time together. r i lie specimen of the regis- 
ter alluded to, which is given Plate Meteoro- 
logy, wi il elucidate the whole of the foregoing 
observations.. 
There is something in these movements of 
the atmosphere very much resembling the 
waves producible in dense fluids. Thus a 
sudden and great depression in the barome- 
ter is follow. d by an equally sudden rise, 
wh.cn is often carried beyond the point from 
Places. 
Years 
of ob- 
serva- 
tion. 
Mean Height of the Barometer. 
Morning. 
Noon. 
Evening. 
Year. 
Arles 
- 
6 
29.9347 
29.9347 
29.9413 
29.9347 ~ 
Arras 
- 
6 
29.6683 
29.6683 
29.6832 
■29.6758 
Bourdeaux 
- 
11 
29.7212 
29.8385 
29.8385 
29.8385 
Cambray 
- 
13 
29 8756 
29.8632 
29.8756 
29.8756 
Chinon 
- 
12 
29.7719 
29.7795 
29.8001 
29.7869 
Dunkirk 
- 
8 
29.9199 
29.9347 
29.9347 
29.9273 
Hagenau 
- 
10 
29.5648 
29.5643 
29.5741 
29.5648 
Laon 
- 
7 
29.3354 
29.3206 
29.3429 
29.3354 
Lisle 
- 
6 
29 9165 
29.9274 
29.9347 
29.9077 
Mayenne 
- 
7 
29.7172 
29.7056 
29.7127 
29.7127 
Manheim 
- 
5 
29.6167 
29.6018 
29.6167 
29.6093 
Montmorenci 
- 
22 
29 6536 
29.6536 
29.6610 
29.6536 
Mulhausen 
- 
7 
29.1873 
29.1800 
29.1873 
29.1873 
Oberuheim 
- 
12 
29.4834 
29.4665 
29.4764 
29.4764 
Paris 
- 
67 
29.8902 
29.8607 
29.8756 
29.8756 
Poitiers 
- 
12 
29.727 6 
29.7276 
29.7276 
29.7276 
Rouen 
- 
11 
29.8607 
29.8535 
29.8535 
29.8535 
Rome 
- 
3 
29.8607 
29.8460 
29.87 56 
29.8607 
St. Maurice le Gerard 
10 
29.801G 
29.8016 
29.8090 
29.8016 
Troyes 
- 
10 
29.6885 
29.6979 
29.6885 
29.6885 
