Part 2 (2/2)
[Ill.u.s.tration: Fig. 2]
LIMITS OF THE VORTEX.
The action of the polar current of the ether, therefore, tends to cause a depression of the barometer, and an elevation to the _northward_ and southward, and there is a general set of the wind below to the point of greatest depression. The action of the tangential current works the outer surface of the atmosphere into great ridges and hollows, whose distances apart as well as actual dimensions, are continually changing under the influences of causes not yet alluded to, and it is in the hollows where the action of the polar current will be princ.i.p.ally expended. Luckily for the earth, the axis of the vortex is never long in pa.s.sing over any particular place. In this lat.i.tude, whose natural cosine is three-fourths, the velocity _westward_ is over 700 miles per hour; but at its extreme limits north, the motion is much slower, and is repeated for two or three days in nearly the same lat.i.tude, for then it begins to return to the south; thus oscillating in about one sidereal period of the moon. At its southern limit, the vortex varies but slowly in lat.i.tude for the same time, but the velocity is much greater. The extreme lat.i.tudes vary at different times with the eccentricity of the lunar orbit, with the place or longitude of the perigee, and with the longitude of the moon's ascending node, but in no case can the _central vortex_ reach within 5 of the equator, or higher than about 75 of lat.i.tude north or south. Hence there are no storms strictly speaking beyond 88[7] of lat.i.tude; although a storm may be raging close by, at the turning point south, and draw in a very strong gale from the northward with a clear sky above. So also, although rains and short squalls may be frequent in the vapor-loaded atmosphere of the equator, yet the hurricane does not reach there, owing to the adjustment of the ma.s.s and distance of the moon, and the inclination of the axes of the vortices to the axis of the earth. If the temperature of the upper limit or highest lat.i.tude of the vortex, was equal to the temperature which obtains at its lowest limit, and the daily extremes of the solar influence as great, the hurricanes would be as violent at the one as the other, and even more so on account of the smaller velocity. But the deficiency of temperature and moisture, (which last is all-important,) prevents the full development of the effect. And even in the tropics, the progress of the sun, by its power in directing the great annual currents of the atmosphere, only conspires in the summer and autumn months, to bring an atmosphere in the track of the vortices, possessing the full degree of moisture and deficiency of electric tension, to produce the derangement necessary to call forth the hurricane in its greatest activity.
ROUTINE OF A STORM.
The novelty and originality of this theory will perhaps justify us in dwelling a little longer on what observation has detected. The vortex (and we are now speaking only of the central vortex) does not derange every place alike, but _skips_ over large tracts of longitude in its progress westward. We speak here of the immovable axis of the vortex as in motion; in reality it is the rotation of the earth which brings every meridian under its influence in some lat.i.tude once every twenty-four hours. The centre of greatest derangement forms the nucleus, towards which the surface currents, under certain restrictions, flow. The strongest current will, however, usually be from the south, on account of the inclination of the axis of the vortex to the surface of the earth.[8] These currents continuing onwards by their vires inertiae, according to the first law of motion, a.s.sist somewhat in conveying the warm surface wind, loaded with moisture, into the region of cloud; and the diminution of temperature causes the condensation of large ma.s.ses of vapor, according to Hutton's views; and the partial vacuum thus produced, causes a still greater intermingling. But we have already shown that this is not the sole cause, nor is it ever more than partially accomplished. The ether of the lower atmosphere, and of the crust of the earth, is disturbed, and rushes towards the rarefied axis from the surface, and with the temperature of the surface, thus conveying the surface atmosphere, in a measure, along with it. In the upper regions, this ether (or electric fluid) cools down, or parts with some of its heat, to the air of those regions, and, by its great specific caloric, necessarily and unduly increases the temperature of the air. This, by its expansion and ascension will cause a further influx from below, until the upper atmosphere becomes loaded with vapor.
In twelve hours, at least, a reaction must take place, as that part of the earth's surface is carried six or seven thousand miles from the axis, where the ether is more dense. This in turn descends to the surface, carrying with it the temperature of s.p.a.ce, at least 60 below zero; a great condensation must follow; local derangements of the electric equilibrium in the centre of large clouds, when the condensation is active, must now take place, while partially nonconducting ma.s.ses intervene, to prevent an instantaneous restoration of the equilibrium, until the derangement is sufficient to cause the necessary tension, when all obstacles are rent asunder, and the ether issues forth, clothed in the power and sublimity of the lightning. It is a fearfully-energetic fluid, and, when sufficiently disturbed, competent to produce the most violent tornado, or the most destructive earthquake.
That these two phenomena have simultaneously occurred, seems well authenticated; but the earthquake, of course, must be referred generally to derangements of the electric equilibrium of the earth's interior, of which at present we know but little.
The day or morning previous to the pa.s.sage of the vortex, is frequently very fine, calm, mild, and sleepy weather,--commonly called a weather breeder. After the storm has fully matured, there is an approach of the clouds to the surface, a reduction of the temperature above, and the human body feels the change far more than is due to the fall of temperature. This is owing to the cold ether requiring so much heat to raise its temperature to that of surrounding bodies, or, in other words, is due to its great specific caloric. In summer, this falling of the upper layers in front of the storm is so apparent, that every part is seen to expand under the eye by perspective,--swelling, and curling, and writhing, like the surface of water or oil when just commenced boiling.
The wind now partakes of the motion of the external ether, and moves with the storm eastward (in this lat.i.tude), or from N-E. to S-E., until the action ceases.
CONDITIONS NECESSARY TO PRODUCE A STORM.
The vortex, in its pa.s.sage round the earth, may only meet with a few localities favorable for producing a very violent storm; but these nuclei will generally be connected by bands of cloudy atmosphere; so that could we view them from the moon, the earth would be belted like the planet Jupiter. There is reason to suspect, also, that there are variations in the energy of the ethereal motions, independent of the conditions of the earth and its atmosphere, which affects even the radial stream of the sun. For the zodiacal light, which is caused by this radial stream, is at times much more vivid than at others. Also in the case of the aurora, on our own globe. On this point there is much to say, but here is not the place. The conditions favorable for the production of a storm at the _central_ pa.s.sage of a vortex, are a previous exemption from excitement _ceteris paribus_, a high temperature and dew point, a depression of the barometer, and local acc.u.mulation of electric tension, positive or negative; and these are influenced by the storms in other places controlling the aerial currents, and thus determining the atmosphere of the place.
LATERAL VORTICES.
We have already alluded to the lateral vortices of the terral system. We must now resort to a diagram.
In the following figure, the arrows represent the ethereal current of the terral vortex; the linear circle, the earth; C the centre of gravity of the earth and moon, and, consequently, the central vortex or axis of the vortex of the earth, I represents the position of the inner vortex, and O that of the outer vortex. These two last are eddies, caused by the obstacle presented by the earth in being _pushed_ out from the centre by the moon, and are called lateral vortices. There are, therefore, two lateral vortices, and one central, in both hemispheres, and by this simple arrangement is the earth watered, and the atmospheric circulation produced.
[Ill.u.s.tration: Fig. 3]
ILl.u.s.tRATION OF THEIR ACTION.
If we place a globe in a vessel of water, so that the vertex shall only just be covered, and place the globe eccentrically in the vessel so that the centre of the vessel may not be too far from the outside of the globe, and then impart an equable but slow motion to the water, in the manner of a vortex; by viewing the reflected light of the sky from the surface of the water above the globe, we shall be able to trace a succession of dimples, originating at I and O, and pa.s.sing off with the current, and dying away. The direction of the fluid in these little eddies, will be the same as the direction of the current in the main vortex. If we displace the globe, so as to remove it far from the centre of the vessel, and impart the same motion, the vortex I will be found at E, and the direction of the current will be contrary to the direction of the fluid in the vessel. In the case of the earth and moon, the displacement can never change the position of the inner vortex much. It will always be to the right hand of the central vortex in north lat.i.tudes, and in consequence of the ether striking our globe in such a position, the current that is deflected from its true path, by the protuberance of the earth forcing it inside, is prevented by the circular current of the parts nearer the axis of the vortex, from pa.s.sing off; so that a vortex is formed, and is more violent, _ceteris paribus_, than the vortex at O.
ORDER OF OCCURRENCE.
Whether this mode of action has been correctly inferred, matters little; the lateral vortices follow the law of such a position. The inner vortex always precedes the central from five to eight days, when ascending in this lat.i.tude, and comes to the meridian after the moon. The outer vortex, on the contrary, follows the central in its monthly round, and comes to the meridian before the moon. It will be readily understood that if the axes of these lateral vortices be produced through the earth, they will pa.s.s through similar vortices in the opposite hemisphere; but as the greatest lat.i.tude of the one, corresponds to the least lat.i.tude of the other, the same calculation will not answer for both. The same remark applies to the central vortex also.
Thus there are six pa.s.sages each month over lat.i.tude 41; but as there are intervals of 3 to 6 between two consecutive pa.s.sages of the same vortex, it may happen that an observer in the middle lat.i.tude, would perhaps see nothing of their effects without looking for them. Generally speaking, they are not only seen, but felt. The time of the pa.s.sage of the outer vortex ascending, corresponds so nearly (in 38 of lat.i.tude) at certain times, with the pa.s.sage of the central vortex descending, that the two may be considered one if attention is not directed to it.
The orbits of these lateral vortices depend, like that of the central vortex, on the orbit of the moon for eccentricity, but the longitudes of the perigee will not correspond with the longitude of the moon's perigee. This follows from the theory. As the elements of these orbits are only approximately determined, we shall confine our calculations to the orbit of the central vortex.
REDFIELD'S THEORY OF STORMS.
It will now appear plainly to the reader, that this theory of storms differs in every particular from the rival theories of Redfield and Espy, both as to the cause and the _modus agendi_. It would appear at first sight, as if the discovery of these vortices would at once remedy the great defect in the theory of Redfield, viz.: that no adequate cause is a.s.signed for the commencement and continuation of the vorticose motion, in the great circular whirlwinds which compose a storm. The facts, however, are adverse to such an application. According to Mr. Redfield, the rotation of a circular storm in the northern hemisphere is from right to left, and the reverse in the southern. The author's attention has, of course, been considerably directed to this point; but in every case he has been unfortunate in finding in the clouds a rotation from left to right. Some cases are mentioned in the appended record of the weather. He has also noticed many of those small whirlwinds on arid plains, in Egypt, in Mexico, and in California, which, in the great majority of cases, were also from left to right. His opportunities, however, have not extended to the southern hemisphere.
This theory has not, however, been formed on theoretic views, but by looking nature in the face for years, and following her indications.
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