ology.

Evils to be anticipated

mea

supersti

109s.

Meteor rooting up what are commonly called popular superstitions, much valuable information may be lost. Many of the common adages respecting the weather, have doubtless had their origin in the observance of Meteorological phenomena; and that Philosopher would but tely root half perform his duty, who, dazzled by the splendid reing out all sults which modern Science now discloses, should abanrecclection don without any examination the traditions that time el popular has handed down. There are some phenomena of the atmosphere, which seem to have suggested to Man in different conditions of his state, ideas and forms of expression of the same common kind. In investigating these, under the dark and shadowy forms which the mutations of language have imparted to them, much important information may be disclosed; and connected as many of them are with cycles and periods of observation, they possess a very high value. Some attempt at a classification of the phenomena to which these traditions relate, would not be unproductive of advantage. Most of them have some foundation in Nature, and it is at least prudent for a Philosopher to keep them in view in the course of his inquiries.

Constitu

(20.) It is thus by watching appearances, and diligently recording phenomena, generalizing observations, and disclosing in their fullest extent the grand system of signs by which Nature works, that Meteorology will advance to that perfection which its ardent cultivators desire.

Constitution of the atmosphere.

(21.) The great volume of the atmosphere is comton of the posed of permanently elastic fluids, the whole of which atmosphere. are retained on the surface of the Earth by the law of gravitation. All eudiometrical processes, when skilfully performed, concur in proving that, apart from the carbonic acid and aqueous vapour which are present in atmospheric air, 100 volumes consist of 79 oxygen, and 21 nitrogen; or, including the two former ingredients, that it is constituted, at a mean temperature and

pressure, of

(22.) It is the business of Chemistry to unfold the delicate processes by which these different relations are determined, and for these we refer the reader to our Essay on that Science; but we may notice here the remarkable fact, that with the exception of the aqueous vapour, the quantity of which varies with the temperature, as will be hereafter explained, the other ingredients of the atmosphere bear at all times, in every region of the globe, whether on the summits of the loftiest mountains, or at the lowest levels of the deepest valleys, the same relative proportion to each every region other. Thus, air from the Alps analyzed by the younger of the Earth. Saussure, from Spain by De Marti, from France and Egypt by Berthollet, from England and the Coast of Guinea by Davy, from the Peak of Teneriffe and from near the summit of the Andes by Humboldt, and from the still loftier elevation of 22,000 feet by Gay Lussac and Thenard, all gave results approaching as nearly as possible to each other.

This constitution the same in

(23.) It has been commonly supposed that the at- Meteormosphere must contain, diffused throughout it, minute ology. portions of the vapours of all those substances with which it is in contact, even down to the earths and metals; and although the unknown ingredients which are occasionally mingled with the atmosphere, and which impart to it deleterious properties, are either of too subtile a nature, or present in too small a proportion, to be discovered by our imperfect instruments, yet Mr. Faraday has shown, in the Philosophical Trans- Mr. Faraactions for 1826, that a limit exists to the production of day's dis vapour of any tension by bodies placed in vacuo, or in covery of a elastic media, beneath which limit they are perfectly porization. fixed.

limit to va

of the at

(24.) Two views have been entertained of the nature Chemical of the union which exists among the several elastic constitution fluids constituting the atmosphere. By the greater mosphere. part of Chemists it has been considered as a Chemical compound, chiefly from the uniform nature of its composition, and from the fact that its several ingredients do not separate and arrange themselves according to their relative Specific Gravities. Mr. Dalton was the first who presented, under a distinct point of view, the remarkable theory, that of the various elastic fluids constituting the atmosphere, the particles of one have Mechanical neither attractive nor repulsive power towards those of another, but that the weight or pressure, upon any one particle of any fluid mixture of this sort, arises solely from the particles of its own kind. According to this hypothesis, oxygen, azotic, and carbonic acid gases may exist together under any pressure, and at any temallotted for all. Each ingredient of the atmosphere, perature, while each of them occupies the whole space according to this view, exerts its own separate pressure forms, says Dr. Henry, the part assigned to it in the in supporting the mercury of the Barometer, and perfollowing table:

constitution of the atmosphere.

stitution of

(25.) In the Philosophical Transactions for 1826, Latest views Mr. Dalton has entered into an extended view of the of Mr. Dalprinciples by which he conceives the constitution of the ton respectatmosphere may be regulated; and to illustrate his ing the conviews, he imagines two equal cylindrical tubes, A and the atmoB, to exist in contact with each other, perpendicular to sphere. the horizon, of indefinite lengths, closed at the bottom, but open at the top. Into the tube A he supposes an atmosphere of hydrogen to be introduced, equivalent to a mercurial column of 30 inches; and into the other tube B, an atmosphere of carbonic acid gas, capable also of supporting a column of 30 inches of quicksilver. Now supposing, he says, these atmospheres to remain, for an instant, of uniform density throughout the extent of each column, and that density to be the same as exists at the surface of the Earth, the altitude of the atmosphere of hydrogen would be about 66 miles, and that of the carbonic acid about 3.3 miles; these heights being to each other nearly in the ratio of 20 to 1. And if these atmospheres be afterwards expanded to their natural extent, equal elasticities of the two gases would

be found to exist at altitudes, also in the ratio of 20 to 1; that is, if at two miles of elevation the atmosphere of carbonic acid supported 15 inches of mercury, that of hydrogen would support the same at 40 miles' elevation. Conceiving now these atmospheres to have acquired their perfect equilibrium, Mr. Dalton imagines numerous air-tight, horizontal partitions to be formed across the tubes, at equal intervals from the ground upwards; these intervals being either a foot or a mile, as may suit our purpose.

(26.) Supposing now a communication to be opened between each two horizontal portions of the tubes, an intermixture of the gases would follow, and finally such an equilibrium be obtained, that one-half of the gas existing at first in each division, would pass into the division opposite, and the other half remain in its original position. The whole weight of the gases in each entire tube would therefore be unchanged, and equivalent as before to 30 inches of mercury, half in each tube being carbonic acid, and half hydrogen gas.

(27.) In tracing the conditions of the gases as we ascend in the tubes, great differences would be found to exist, both as regards volume and weight. In the lowest division we should find equal volumes of carbonic acid and of hydrogen. At the height of two miles, one volume of the former gas would be found mixed with two of the latter; at four miles' elevation, the carbonic acid would be to the hydrogen nearly as one to four; and at 40 miles all the carbonic acid will have probably disappeared, but the hydrogen would remain of one-half its density in the primitive cell. Above the limits of the carbonic acid, wherever it may be, nothing but hydrogen gas would be found in each tube, up to the limits of the hydrogen atmosphere.

(28.) After a complete equilibrium has taken place between every two adjacent cells, Mr. Dalton conceives the horizontal divisions to be withdrawn. The descent of the upper part of the hydrogen column in each tube will be immediate, as there will be vacuities to be filled up in it. The same would take place in the column of carbonic acid, but the great body or weight of the mixed atmospheres would remain unchanged, excepting a slight condensation. The column of hydrogen in each tube would support 15 inches of mercury, and in all respects would resemble the upper half of the first column A, of hydrogen, that supported 30 inches, excepting a slight difference occasioned by distance from the earth and temperature; and the same may be said of the carbonic acid column in each tube.

(29.) But would this constitution of the mixture, Mr. Dalton asks, be permanent? Would a mixed atmosphere, which, in fact, as a whole, consisted of equal weights of carbonic acid and hydrogen, continue to exhibit, at the surface of the Earth, equal volumes only in mixture? Or, on the other hand, would not the whole be wrought up in due time into one uniform composition in all its extent, of twenty volumes of hydrogen with one of carbonic acid, as many suppose to be the nature of the Earth's atmosphere with regard to its component parts? To these questions, Mr. Dalton replies, by observing, that from what we know of the nature of mixed gases, each of the two gases would be disposed in the same manner as if the other was not present. They would be mixed in equal volumes at the Earth's surface; the carbonic acid would rapidly diminish in density as it ascends, terminating perhaps at 28 or 30 miles of elevation; and the hydrogen would slowly

diminish in density, terminating perhaps at an altitude Meteorof eleven or twelve hundred miles. ology.

(30.) In applying this doctrine to the Earth's atmosphere, supposing it to be in a quiescent state, Mr. Dalton neglects the carbonic acid and aqueous vapour, as inconsiderable in weight, and fixing the weight of the atmosphere at 30 inches of Mercury, he finds of 30-6.3 inches, for the weight of the oxygenous atmosphere; and of 30= 23.7 inches, for the weight of the atmosphere of azote, since the weights of the respective atmospheres in this view are proportional to the volumes found at the surface of the Earth, and totally independent of their Specific Gravities. The weight of the aqueous vapour being variable, he fixes at 0.4 inches of mercury, and that of the carbonic acid at 0.03 inches.

(31.) This train of investigation has been conducted on the supposition of a quiescent atmosphere, or of one in a state of perfect equilibrium. How the case would be with regard to the Earth's atmosphere, such as it actually is, in a state of continual agitation, it is not easy to ascertain; and it is besides, says Mr. Dalton, rather a question to be decided by experiment and observation than by theory. Mr. Dalton, it appears, has a series of observations already made on this important subject; and he has promised to add them, as a supplement, to the paper from which these interesting extracts have been made.

(32.) The labours of Mr. Dalton, on the constitution of the atmosphere, have become the foundation of much of our knowledge in this important department of Science; and, accordingly, Mr. Daniell, the latest writer Inquiries of on the subject, has grounded his inquiries entirely on Mr. Daniell. the principles established by the Manchester Philosopher. In his Essays on the Constitution of the Atmosphere, Mr. Daniell has divided his inquiries into four branches. In the first part, investigating the habitudes Division of an atmosphere of perfectly dry, permanently elastic into four fluid, under particular conditions; in the second, those parts. of an atmosphere of pure, aqueous vapour; in the third, the compound relations arising from a mixture of the two; and in the fourth, the application of such principles as the former sections of his inquiry may have disclosed, to some of the observed phenomena of the atmosphere of

the earth.

of the first

(33.) In tracing the habitudes of an atmosphere of Investigaperfectly dry, permanently elastic fluid, surrounding a tion of the sphere in a state of rest, of uniform temperature in all conditions its parts, and to the centre of which it gravitates part, the equally, Mr. Daniell first shows that its height, density, temperature and elasticity must be everywhere equal at equal uniform. elevations; and that the column of mercury which it would support in the Barometer, would be everywhere the same at the surface of the sphere. This is a necessary consequence of the law of Hydrostatics. The second condition is, that its density must decrease in a geometrical progression, in ascending through equal stages to its higher regions, because the density must be everywhere proportional to the superincumbent weight; and, thirdly, that its sensible heat must decrease progressively from below upwards.

(34.) Mr. Daniell next supposes the temperature The temof the sphere to rise generally and equally in all its perature to rise geneparts, and traces the consequent increase of elasticity, rally and and total augmentation of height. There being no equally in alteration in the ponderable matter of the vertical sec- all its parts. tions into which the atmosphere may be supposed to

Temperature to in

ecal incre

(35.) Advancing a step higher in his inquiry, Mr. Daniell next imagines the temperature of the sphere crease by round which the atmosphere is diffused, to increase by ets from equal increments from the Poles to the Equator; and He Poles to assuming zero for the temperature at the former, supEquator. poses that of the latter to be 80°. By limiting the pressure of the atmosphere to 30 inches of mercury at all parts of the surface of this sphere, the elasticity of the air must remain constant, but its Specific Gravity at the Poles will be much greater than at the Equator, and hence the atmospheric column in the Polar regions must be proportionally shorter than that in the Equatorial.

Pear and

(36.) The unequal densities of the aerial columns Equatorial must produce a current from the Poles to the Equator; currents. but as the difference of gravity becomes less as we ascend from the surface, and at a certain point is neutralized; so, on the other hand, the elasticity, which is constant at the surface, varies with the height; and the barometer stands higher, at equal elevations, in the equatorial than in the Polar column. This disproportion increasing with the elevation must, at some definite elevation, much more than compensate for the

unequal density of the lower strata, and thus occasion Meteora counter-flux from the Equator to the Poles. ology.

(37.) These differences of gravity and elasticity may be regarded as distinct and opposite powers, their forces being measured upon the same scale. The excess of gravity may be estimated from the consideration, that the pressures of equal columns are as their Specific Gravities; and as, by Mr. Daniell's supposition, this excess of gravity is unopposed at the surface of the sphere by any excess of elasticity, so is it the exact measure of the force with which a Polar atmosphere would press upon an Equatorial, supposing the two in juxtaposition. The same excess of gravity is also the measure of the pressure which would be required at the Equator to equalize its density with that of the Poles. Could this increase of pressure actually take place, the aerial current would be reversed, and flow with the same force from the Equator to the Poles, the current being now occasioned by excess of elasticity, as it was before caused by excess of gravity.

(38.) After assigning limits to the elevations of these Illustrative currents, Mr. Daniell proceeds to estimate their velo- Table. cities, and then furnishes, as in the following Table, the elasticity, Specific Gravity, and temperature of such an atmosphere, calculated upon his peculiar data, for every ten degrees of latitude, from the surface, by equal altitudes, to the height of 30,000 feet.

14.119.531.65639

0

15000

20000

25000

30000

7.6

8.483.31980-30.7

70.4 30.000.90625 76.8 30.000.90000 54.5 24.319.76160 61.1 24.342.75737

89

80

64.4

48.4

31.4

Meteor. ology.

Height.

Meteorology.'

5000

+.178+.178

+.387+.387

+.810+.810

+1.034 +1.034

10000

15000

20000

25000

30000

,093.260+.176.084-.296.261

+.570

+.217

-.035

-.239

-.272-.336 +.029 -.307

-.036 -.322

(40.) It may be remarked, with reference to these the preced- Tables, that a change of temperature, which equally ing Tables, pervades a column of air throughout its whole length, may effect an adjustment of density without disturbing the equiponderant mercurial column situated at its base; but the force of the compensating currents will be altered, and, under some circumstances, their courses even changed. An alteration of temperature, for example, in latitude 50°, will increase the force of the current from latitude 60° to 50° in its original direction, while that from 50° to 40° will be reversed: the wind, which had blown on the surface between the former parallels with a force of 0.810 inches, being increased to 2.560 inches; and that which moved between the latter parallels with a force of 1.034 inches, blowing now in the opposite directions with a force of 0.840 inches. Corresponding changes of velocity and direction ensue in the upper currents, and thus the compensation of pressure takes place.

Effects of an

(41.) Any cause also which tends to diminish gradually the Specific Gravity of a permanently elastic fluid column at its base, or, on the contrary, to augment its temperature at its superior limit, will affect it through its entire length; so that, if its heat be slowly increased below, its temperature must rise from one extremity to the other, and vice versa. But although such a change may take place, without increasing the length of the mercurial column at its lower extremity, at all higher stations the Barometer will rise.

(42.) Let us next follow Mr. Daniell, when he imaincrease of gines heat to be communicated to the upper strata of temperature of the upper his atmosphere, and which, from some temporary strata of the cause, does not originate in, or extend to the lower. atmosphere. For this purpose, he supposes some increase of temperature at a definite altitude. The influence of the

-Upper Equatorial Current.

heat communicated will be felt in the superior strata, but those in the lower regions must, by the supposition, remain unchanged. The first effect which results will be an augmentation of elasticity in the upper beds of the atmosphere, which, exerting its force upon the high Equatorial current, will accelerate its velocity on one side, and diminish it on the other. The expanding air, not being laterally confined by a proportionate expansion of the neighbouring sections, will not accumulate above, but, flowing off, will cease its vertical pressure upon that column. The upper regions, therefore, will be rarefied, and become lighter, and pressing with less weight upon the lower, the Barometer will fall at the surface of the sphere, in proportion to the degree of expansion. The density of an elastic fluid being the result of its gravity acting upon its elasticity, by the reaction of these powers, any change in the vertical column must be communicated instantaneously throughout its entire length, and no inequality of density can for a moment exist.

a definite

(43.) To generalize still further, let us again imagine Local acwith Mr. Daniell, the local accession of heat, instead cession of of pervading at once the whole of either horizontal sec- heat, com tion, to commence at some definite point, and gradually mencing a extend itself in depth. The disturbing cause will then point, and affect the lower current, and the expanding volumes gradually of air, not being checked by a simultaneous increase of extending elasticity in the adjoining columns, will rush forward in depth. with accelerated velocity, and the diminution of density occasioned by the excessive drain will be distributed throughout the column by mechanical adjustment. The fall of the Barometer would be proportionate to the extent to which the rise of temperature would reach in this progressive manner. A small increase, thus operating, will produce the same amount of depression, as

Barometer is exhibited of a small partial increase of temperature, gradually extending itself throughout the aerial column, in conformity to the preceding changes.

Table.

Meteorology.

tion of the currents.

+.63 +1.44 +2.07 +.26 +1.09 +1.35|| +.12 +0.81 +0.93 +.02 +0.60 +0.62||

+.63 0. +0.63 +.47 +0.08 +0.55

+.46 +0.14 +0.60

Remarks.

From latitude 40 to 30, it will be observed, that the force of the Polar current is greatly increased; while from 30 to 20, the effect is entirely reversed.

(46.) It may readily be imagined, continues Mr. Daniell, that irregularities thus introduced into these compensating movements, the consequence of diminished mechanical pressure, must of themselves be liable to produce changes of temperature in the atmospheric columns, foreign to the natural gradation; and that, amongst others, the atmosphere, in its upper parts, may be liable to greater depressions of heat than would result from the elevation alone. A gradual process of cooling taking place in the higher portions of a body of air, would communicate itself to the whole mass, in an analogous manner to the equal diffusion which would ensue from the slow communication of heat to the lower parts; that is to say, without producing any effect upon the Barometer at the surface of the sphere, or any irregularity in the gradation of temperature. But where the change is effected suddenly, by the admixture of a large body of cold air, a mechanical effect is produced by the increased pressure of the mass; and the

VOL. V.

-

+.39 +0.18+0.57 +.34 +0.20 +0.54 +.33 +0.21 +0.54 +.33 +0.22+0.55

equilibrium of density takes place before the adjustment of temperature. An atmosphere hence results, the heat of which decreases in a greater proportion than is due to the decrease of density; and the effect is analogous to that which arises from an irregular increase; and the Barometer must also rise to equalize the specific gravity.

(47.) It is not required here that we should point out all the means by which such changes of heat as we have alluded to may be effected, or that we should trace further the endless modifications of densities and currents which would result from their different applications. It is sufficient, says Mr. Daniell, at present, to have shown that, supposing them to arise, certain general consequences must follow.

(48.) In the preceding review of the labours of Mr. Daniell, we have found that he has contemplated the various changes that have been alluded to, with reference Effects of to the particular column of the atmosphere in which the precedthey had their origin. We shall now make our readers ing changes acquainted with his estimate of their effects those upon with which they are connected. For this purpose, we lumns of the must remember, that it has been established as a prin- atmosphere.

C

upon the ad jacent co