METEOROLOGY.
525 '
Jl'e moon’s nodes; but the observations on which this opinion is"uilt are by no means sufficient to establish it, and the dissimila-rit y between the phenomena of different years sufficiently war-ra »ts us to conclude, that other causes, besides the regular actionthe sun and revolution of the earth, arc concerned. Some oflll ese causes have been supposed to be fermentations and otherc °mmotions within the bowels of the earth itself, but the immense'ariety which occurs in meteorological appearances can by noffieans be accounted for by the interference of such causes. Buta little attention to the subject will lead us to conclude that thesePhenomena are the consequences of chemical action by whichPere is a continual and rapid succession of new combinations and^compositions. “ Though’the phenomena of the weather, saysjr r - Thomson, must have at all times attracted much of the atten-*°n of mankind, because their subsistence and their comfort in apeat measure depended upon them, it was not till the 17th cen-p r y> that any considerable progress was made in investigating the| aw « of meteorology. How desirous soever the ancients mightlave been to acquire an accurate knowledge of this science, theiry'ant of proper instruments entirely precluded them from cnltivat-,?S If' By the discovery of the barometer and thermometer, inhe 17th century, and the invention of accurate electrometers andygrometers in the 18lh,. this defect is now pretty well supplied ;hd philosophers are enabled to make meteorological observationsv dn ease and accuracy. Accordingly a very great number ofhch observations have been collected, which have been arrangedhd examined from time to time by ingenious men, and conse-quences deduced from them, on which several different theoriesthe weather have been built. But meteorology is a science sopceedingly difficult, that notwithstanding the united exertions of°>ne of the first philosophers of the age, the phenomena of theeather are still very far from being completely understood; nor can® expect to see the veil removed, till accurate tables of observa-°ns have been obtained from every part of the world, till the at-'osphere has been more completely explored, and the chemical,‘ a »ges which take place in it ascertained. The changes, whichplace in the atmosphere demonstrate, in the clearest manner,« hew combinations and decompositions are continually goingt e ln On these chemical alterations, the greater number of me-r 0r p°gical phenomena depend : they may be considered as theSu u of the mutual action of the different component parts of thetl^sphere ; and would admit of an easy explanation, if we werew r ° u ghly acquainted with all these substances, and with the che-utol - aws which govern their action. The most important mete-th e °’. ca l phenomena are, 1. The changes which take place inin f" e 'Sht of the atmosphere. 2. The changes wdiich take placep ' . temperature. 3. The fogs, clouds, and rain, which so oftenth r Cl Pitate from it. 4. The violent agitation into which it is oftenc 0 ° Wn : and, 5. The electric phenomena which sometimes ac-< ; 0 f 1 P a ny or occasion these precipitations and agitations. Thein asic ‘ e rations of these phenomena shall occupy the five follow-
8 sections.”
Op the Changes in the Weight op the Atmo-
SPHERE.
tvf barometer indicates to us the weight of a column of air,Aiendin--- - - . - —i—-
that" f' n ® t° the top of the atmosphere, and whose base is equal toai r : °‘ the mercury. At the level of the sea, where the column oft his e° n U est: > the mean height of the barometer is thirty inches.i'a n * lr George Shuckburgh found to be the case in the Mediter-ll 0u an ai 'd the Channel, in the temperature of 55° and 60°; M.tavfH*. 011 the coast of Peru , in that of 84°; and Lord Mul-hi»i® In ‘at 30°. The mean height of the barometer is less, thecdj u * any place is situated above the level of the sea, bec ause theh-Wi °‘ a ’ r which supports the mercury is the shorter. 'Fhe‘' A Ro leter *' as accordingly been used for measuring heights. Seep!a Ce But if a barometer be allowed to remain in one
and mercury does not remain stationary ; sometimes it rises,c °tir$e h ' er tlmes falls, varying to the extent of several inches; ofObject, weight of the air, which balances the mercury must beSai he nt. same cluing es. lienee we learn, that the air in thet!) ce s «,p e ,' s sometimes light, and at other times heavy; differ-hteter tl* • mi ' s ‘ ‘ Je o.ving to changes in its quantity, 'File haro-
‘>abl e t 0 ' en ' n t orms us > that the Quantity of air above any spot isVot . con t>nual alterations. Consequently either the air accu-* 111 —No. 142.
initiates in particular spots,, while it partially abandons others; orpart of the atmosphere must be alternately abstracted altogether,and restored again by some constant, though apparently irregular,process. Between the tropics the variations of the barometer areexceedingly small; and it is remarkable, that, in that part of theworld, it does not descend above half as much for every 200 feetof elevation as it does beyond the tropics. In the torrid zone,too, the barometer is elevated about two-thirds of a line twiceevery day ; and this elevation happens at the same time with thetides of the sea. As the latitude advances towards the poles therange of the barometer gradually increases, till at last it amountsto two or three inches. This gradual increase will appear fromthe following table:
Table of the Range of the Barometer.
Lat.
Places.
Greatest R.
Annual R.
0®
/
0.20
--
22
23
Calcutta
0,77
—
40
55
Naples
1.00
—
51
8
Dover
2.47
1.80
53
13
Middlewick
3.00
1.94
53
23
Liverpool
2.89
1.96
59
56
Petersburg!!
3.45
2.77
“ In North America , however, the range of the barometer is agreat deal less than in the corresponding European latitudes. InVirginia , for instance, it never exceeds 1.1. It is greater at thelevel of the sea than on the mountains, and in the same degree oflatitude the extent of the range is in the inverse ratio of the heightof the place above the level of the sea. From a table publishedby M. Colte in the Journal de Physique, (for Aug. 1790, p. 110,)it seems exceedingly probable that the barometer lias always atendency to rise from the morning to the evening ; and that thistendency is greatest between two o’clock P. M. and nine at night,at which hour the greatest elevation takes place ; that the eleva-tion of nine o’clock differs from that of two by four-twelfths, whilethat at two differs from the morning-elevation only by one-twelfth; and that in certain climates the greatest elevation takesplace at two o’clock.”
The following is a part of the Table on which tiiese observation*are founded, reduced to the English standard.
Places.
Yearsof ob-serva-tion.
Mean Height of the Barometer.
Morn.
Noon.
Even.
Year.
6
29.9347
29.9347
29.9413
29.9347
Arras .
6
29.6683
29.6683
29.6832
29.675S
Bourdeaux .
11
29.7212
29.8385
29.8385
29.8385
13
29.8756
29.8682
20 87S6
Cbiuon .
12
29.7719
29.7795
29.8001
29.7869
Dunkirk...
8
29.9199
29.9347
29.9347
29.9273
Ilagenau.
10
29.5648
29.5648
29.5741
29.5648
7
29.3354
29.3206
29.3429
29-3354
Lisle .
6
29.9165
29.9274l29.9347
29.9077
7
29.7172
29.7056'29.7127
29.7127
Manheim.
5
29.6167
29.6018
2.9.6167
29.6093
22
29.6536
29.6536
29.6610
29.6536
M ulhausen.
7
29.1873
29.1800
29.1873
29.1873
Obernheim.
12
29.4834
29.4665
29.4764
29.4764
Paris .
67
29.8902
29.8607
29.8756
29.8756
12
29.7276
29.7276
29.7276
29.7276
Rouen.
11
29.8607
29.8535 29.8535
29.8535
Rome .
3
29.8607
29.8460
29.8756
29.8607
St. Maurice le Gerard.
10
29.8016
29.801629.8090
29.8016
Troyes.
10
29.6885
29.697929.6885
29.6885
__ “ The range of the barometer (continues Dr. Thomson,) isgreater in winter than in summer. '1 bus at York, the mean rangeof the barometer, during October, November, December, Ja-nuary, February, and March, 1774, was 1.42; and for the six
summer-months* 1.016. In serene and settled weather it L gene-ts S rally