Another unexplained phenomenon is the corruscation of the tail. It has been attempted to explode this fact also, by referring it to conditions of our own atmosphere; and it is generally considered the argument of Olbers, founded on the great length of the tail and the velocity of light, is sufficient to prove that these corruscations are not actually in the tail. Now, it is undoubtedly true, that as light travels less than two hundred thousand miles in a second, and a comet"s tail is frequently one hundred millions long, it is impossible to see an instantaneous motion along the whole line of the tail; but granting that there are such flickerings in the tail as are described by so many, it must necessarily be, that these flickerings will be _visible_. It would be wonderful indeed, if a series of waves pa.s.sing from the comet to the extremity of the tail, should have their phases so exactly harmonizing with their respective distances as to produce a uniform steady light from a light in rapid motion. The argument, therefore, proves too much, and as it is in the very nature of electric light thus to corruscate, as we see frequently in the northern lights, we must be permitted still to believe that not only the tails, but also the heads of comets do really corruscate as described.
With respect to the direction of the tail, astronomers have been forced to abandon the antiquated notion, that the tail always pointed directly from the sun; yet they still pertinaciously cling to the idea, that although this is not always the case, the tail only deviates from this direction _in the plane of the orbit_. As this is a most important question, it is necessary formally to protest against such a conclusion.
If the earth should happen to be in the plane of the comet"s...o...b..t and the tail appears in that plane, it must of course be in that plane _really_; but if the earth is not in the plane of the comet"s...o...b..t, the tail is not _necessarily_ in the same plane, whatever its apparent direction may indicate. It is true there is a tendency of every particle of the tail, moving under the restraining influence of the sun"s attraction, to continue in the plane of the orbit; and in certain positions there is no oblique action arising from the force of the radial stream to cause it to deviate from that plane; yet in other positions of the comet, the action of the radial stream may be oblique, forcing it out of that plane, and still such a direction might be a.s.signed to it as to make it conform. In the comet of 1843, P. Smythe observed a forked tail 25 long on March 3d, and from the end of the forked tail, and from its _north_ side, a streamer diverged at an angle of 6 or 7 to the _north_. As this was contrary to the _direction_ of the curvature, if the tail had been curved, it could only arise from a portion being driven off by the radial stream, or bent towards the plane of the ecliptic. The curvature observed by others at a later date, was concave to the south. Towards the middle and close of March, the tail became straight, and with the above exception, might be considered to move in the plane of the orbit.
The celebrated comet of Halley, as observed by Dr. Bessel in 1835, showed that a more or less well-defined tuft of rays emanated from that part of the nucleus which was turned towards the sun; and the rays being _bent backward_ formed a part of the tail. The nucleus, with its emanations, presented the appearance of a burning rocket, the end of which was turned sideways by the force of the wind. And, Bessel concludes: "That the cone of light issuing from the comet deviated considerably both to the right and left of the true direction of the sun, but that it always returned to that direction, and pa.s.sed over to the opposite side; so that the cone of light, and the body of the comet from whence it emanated, experienced a rotatory, or, rather, a vibrating motion _in the plane of the orbit_." It is impossible that Bessel should here mean that this motion was certainly in the plane of the orbit; for the orbit was then viewed sideways, and he had no means of ascertaining the fact. His meaning must be that it was apparently in the plane of the orbit. If a plane be made to pa.s.s through the earth, the comet, and the sun, the tail might be placed in any position in that plane, and yet appear to be at the intersection of the two; that is, in the plane of the comet"s...o...b..t. The vibration of the tail, in this case, is another strong proof of the correctness of our theory. To make it more intelligible, we shall resort to a diagram.
In the following diagram, the comet"s...o...b..t, represented by the dotted line, is drawn on the plane of the ecliptic; it is, therefore, necessary to bear in mind, that it is tilted up from the line of nodes SN, at an angle of 17 45". The position of the comet, October 9th, is at C, approaching its perihelion; that of the earth at the same time at T; while S represents the sun, and SQ the line of equinoxes. Now, from a cause already explained, the tail always tends to lay behind the comet, in the direction indicated by the lower tail in the diagram at 1, and, if produced, would pa.s.s to the left of the sun, as seen from the earth: the force of the radial stream, however, will not allow this lagging of the tail, and it is straightened out by this force; but, being directed to the axis of the vortex, and not to the sun, it is not really in the plane of the orbit, but is seen in the direction of the upper tail depicted in the diagram at 3, and, if produced, would pa.s.s to the right of the sun, as seen from T. Now, there is an intermediate position of the tail, in which it will appear in the prolongation of the radius vector SC; this position is represented by the middle or central tail of the comet at 2, yet this is not in the plane of the orbit, it only appears to be, as may be readily understood by remembering that the earth at this time is under this plane, and the comet is seen at a considerable elevation above the plane of the ecliptic. When the comet"s tail becomes directed to the axis of the vortex, or in the _apparent_ position of No. 3, the comet, rapidly careering on its way to the sun, again leaves the tail behind, and again it is strengthened out by the radial stream oscillating about the mean position at 2, as observed by Bessel. From this, it appears, that there is no necessity to make confusion worse confounded, by resorting to polar forces, which are about as intelligible as the foundations of the pillars of Atlas.
[Ill.u.s.tration: Fig. 25]
It may be objected that the continued action of the radial stream with that velocity we have contended for, ought to keep the tail invariably directed from the axis of the vortex; but, where there are two forces or tendencies, as in this case, a.n.a.logy would teach us that a certain degree of oscillation is a necessary result. There may, also, be slight and transient changes in the direction of the radial stream. In the hurricane there are short and fitful blasts inclined to the general direction of the wind, which must arise from the inertia of the moving ma.s.s of atmosphere, causing temporary condensations and rarefactions. Be this as it may, we have a.s.signed a cause which satisfies the phenomenon, without coming into collision with a single principle of celestial mechanics.
Prof. Struve compared the tail of this comet to a flame, or "ray of fire shot out from the nucleus, as from some engine of artillery, and driven on one side by the wind." At the same time, he saw a second emanation nearly in the opposite direction. This last might arise from a momentary fluctuation in the relative intensities of the electric radiation of the comet, and of the radial stream, owing to the probable irregularities just alluded to. Such and kindred phenomena are utterly inexplicable, without we adopt the theory we are advocating. One other feature, and we will leave the subject.
From our explanation of the solar spots, we inferred the existence of another large planet in the system. Might not the same effect be produced by a comet? Or may there not be so many comets, whose great elongation, combined with even a moderate ma.s.s, may render it impossible to calculate the position of the sun with respect to the central axis of the vortex,--always considering this last as the axis of equilibrium? In a general way, we might say that the very number of comets in all directions and all distances, would tend to neutralize each other"s effects; but we are not under this necessity. A comet, moving in a parabola, does not belong to the system or to the rotating vortex; and the periodic comets, if of gaseous elements, (as seems so probable,) must, from the size of their nuclei, which the theory considers the only part const.i.tuting their ma.s.s, have far less ma.s.s than the very smallest of the asteroids, and consequently could have very little effect on the mechanical balance of the vortex, even if elongated as far as the orbit of Neptune. Did we know the influence of cold in limiting the expansibility of the elementary gases, we might approximately determine the ma.s.s of a comet, from the size of its nucleus; but this is a problem that has never yet been solved; and astronomers ought to avail themselves of every indication which promises to realize this great desideratum. The grand comet of 1556 is now probably approaching, and, from recent investigations, it appears that it will arrive at its perihelion in 1858,--subject to an error either way of about two years.
An opportunity may thus be presented of determining the ma.s.s of one of the largest comets on record, which may not again occur. This arises from the possible appulse of the comet to the planet Pallas, whose ma.s.s, being so small, would more sensibly be disturbed by such an appulse than the earth. As the inclinations and ascending nodes of the two orbits approximately coincide, and as Pallas will be near the comet"s path, on the approach of the latter to the sun, at the beginning of the year 1857, should the comet become visible about that time, a very close appulse is possible. It is not unlikely, also, that if the elements of Pallas were so far perfected as to afford reliable indications, that the near approach of the comet might thus be heralded in advance, and lead to an earlier detection of its presence. Would it not be a worthy contribution to science, for some one possessing the necessary leisure, to give an ephemeris of the planet for that epoch; as a very slight change in Mr. Hind"s elements of the comet, would cause an actual intersection of the two orbits in about heliocentric longitude 153? The subsequent nodal pa.s.sage of Pallas will take place near opposition, and be very favorably situated for determining the instant of its pa.s.sage; and, of all the elements, this would be more likely to be affected than any other.[47]
THE ZODIAL LIGHT.
A phenomenon, akin to that which we have just been considering, is presented by that great cone of diffused light which accompanies the sun, and which in tropical climes displays a brilliancy seldom witnessed in high lat.i.tudes, on account of its greater deviation from the perpendicular. Sir John Herschel conjectures that it may be "no other than the denser part of that medium, which, as we have reason to believe, resists the motion, of comets,--loaded, perhaps, with the actual materials of the tails of millions of those bodies, of which they have been stripped in their successive perihelion pa.s.sages, and which may be slowly subsiding into the sun." If these materials have been stripped, it is due to some force; and the same force would scarcely permit them to subside into the sun. Once stripped, these portions must be borne outwards, by the radial stream, to the outer verge of the system. Still, there are, no doubt, denser particles of matter, of the average atomic density of Mercury and Venus, which can maintain their ground against the radial stream, and continue to circulate near the central plane of the vortex, in all that s.p.a.ce between the earth and the sun. But if the zodial light be the denser part of that medium, which astronomers now generally recognize as a resisting medium, how happens it that it should be confined to the plane of the ecliptic? Why should it not be a globular atmosphere? Here, again, our theory steps in with a triumphant explanation; for while it permits the acc.u.mulation of such particles around the equatorial plane of the sun, it allows no resting-place very far removed from this plane. The zodial light, therefore, is not the resisting medium, but the pa.s.sage of the radial stream through a diffuse nebula of atoms, brought down the poles of the vortex by the polar current, and held in check along the central plane by gravitation.
If these atoms partook of the velocity of the ether, they would not be luminous; but being held back by gravitation, they are opposed to the radial stream, and hence the light.
Many stars are also nebulous. In some cases we see the nebulosity edgewise, or along the equatorial planes of the stellar vortices; in others we look down the poles, and the nebulosities are circular, and there is an endless variety in the shape and intensity of this light.
But the universe seems full of motion, and we are not justified in supposing, because a star shows no such light, that it is without rotation. The parallax of the nearest star is only one second, the whole lenticular ma.s.s of light which surrounds our sun would therefore only subtend an angle of a single second at the nearest fixed star. Seeing its extreme faintness, therefore, the effulgence of the star would render it totally invisible, provided that it _could_ traverse the vast immensity of intervening s.p.a.ce, without feeling the influence of that extinction, which Struve has proved does actually diminish the number of visible stars.
Corruscations and flickerings have also been noticed in the zodial light, and as usual, the learned have suggested atmospheric conditions as the cause, instead of trusting to the evidence of their own senses.
How p.r.o.ne is philosophy to cling to that which is enveloped in the mist of uncertainty, rather than embrace the _too simple_ indications of nature. As if G.o.d had only intended her glories to be revealed to a favored few, and not to mankind at large. Blessed will be the day when _all_ will appreciate their own powers and privileges, and no longer regard the oracles which emanate from a professional priesthood, whose dicta have so often tended to darken the simple counsels of truth! To set the question of pulsations in the zodial light, as well as in the tails of comets, at rest, only requires previously concerted observations, in places not very widely apart; for it is scarcely possible, that atmospheric conditions should produce simultaneous pulsations in two distant places. If the pulsations are found to be simultaneous, they are real; if not simultaneous, they may depend on such conditions; but from the nature of the cause, we should look for them as much in the zodial light, as in the aurora borealis, regarding the different intensities.
There is also reason to suspect that the northern side is always the brightest, both in spring and autumn. On the morning of October 4th, 1853, the light was very vivid and well defined, its northern margin grazing Regulus and terminating at Mars, which was also to the north of it. Now, although the _northern side_ was the brightest, the great ma.s.s of light was to the south of the ecliptic, as far down as the cone shape was preserved; but at 10 from the horizon, a still brighter ma.s.s protruded from the cone towards the north, which was all _north_ of the ecliptic, and of an irregular form, extending along the horizon. The time was 4 A.M., and consequently was not due to any crepuscular light.
An explanation of the general fact of the brightest light being _always_ on the north side, is given in the present section, in connection with another phenomenon. If, as some suppose, the light does not reach to the sun, the annulus must at least fill all the s.p.a.ce between Venus and the earth, but it is far more in accordance with facts as well as with our theory, to suppose it increases in density to the body of the sun.
Observations made at the observatory of the British a.s.sociation, detected, in 1850, sudden brightenings of the light, altogether different from pulsations. The theory would refer these to that fitful irregularity in the momentary intensity of the radial stream, which gives the flickering and tremulous motion to comets" tails. But, the steady variations in the intensity of this light must be due to other causes. The longitude of the sun will here come in as a modifying cause; for the obstruction caused by the body of the sun, when displaced from the axis of the vortex, must necessarily exercise an influence on the force and direction of the radial stream. A sudden influx of cometary matter down the poles of the vortex, in more than usual quant.i.ties, will also tend to brighten and enlarge the zodial light; and, in this last cause, we have an explanation not only of ancient obscurations of the solar light, but, also, of those phosph.o.r.escent mists, such as occurred in 1743 and 1831, rendering moonless nights so light that the smallest print could be read at midnight.
In total eclipses of the sun, the denser portion of the zodial light is visible as a brilliant corona; but, on such occasions, the brightest stars only are to be seen, and, consequently, the fainter portions of the light must be invisible. Hind mentions as many as ten stars visible in the total eclipse of 1842. According to the same authority, the color of the corona was like tarnished silver, and rays of light diverged in every direction, and appeared shining through the light of the corona in the total eclipse of 1851. In this year on the day of the eclipse (July 28th), the longitude of the sun was about 340, and, therefore, the body of the sun obstructed the radial stream as seen from the earth on the right side; but, in 1842, the longitude of the sun was, according to our table, about 116, the sun"s centre then being 700,000 miles from the axis of the vortex, and on the opposite side with respect to the earth; the position was, therefore, not so favorable for the appearance of these rays which, in many cases, have given the appearance of a whirling motion to the corona.
At this date, July 7th, 1842, the corona, according to Prof. Airy, "possibly had a somewhat radial appearance, but not sufficiently marked to interfere with the general annular structure." Mr. Baily, on the contrary, says, the corona had the appearance of brilliant rays; and, at Milan, long jets of light were particularly noticed. There can be no doubt but that the pa.s.sage of the radial stream past the outer margin of the moon must also give rise to the same phenomena as when pa.s.sing the sun, and in this we have an explanation of the fact, that, previous to the moment of first contact, an appearance resembling a faintly-illuminated limb of the moon, has been perceived near the body of the sun; as well as of those flashes of light which have been observed in the lunar disc as the eclipse advances. One important fact, worthy of note, is, that these luminous streaks are more nearly parallel than is due to a radiation from the centre. These streaks have, also, been seen bent at right angles at the middle of their height, as a flame is by means of a blowpipe, precisely a.n.a.logous to cometary rays being driven backwards to form the tail, as already described, thus indicating a common origin. If the moon had an atmosphere, we should, no doubt, see a greater display; but, having no rotating vortex to protect her from the radial stream, her atmosphere must have been long since stripped off, leaving her exposed to the withering winter blast of the great stream of the solar vortex. In this connection, we may also allude to the appearance of the moon when totally eclipsed. Instead of disappearing at these times, she sometimes shines bright enough to reveal her smallest spots. This has been generally referred to the refraction of the earth"s atmosphere bending inwards the solar rays. May it not be owing to the brilliancy of the solar corona, which, in 1842, was described as so intense that the eye was scarcely able to support it? This is a far more palpable cause for the production of this phenomenon, but of which astronomers cannot avail themselves, as long as they are uncertain of the origin of this corona.
SHOOTING STARS.
The continual influx of cosmical matter into the heart of the vortex in ever-varying quant.i.ties, and speedily dispersed along the central plane, according to its density, must necessarily give rise to another phenomenon to which we have not yet alluded. Scarcely a night pa.s.ses without exhibiting this phenomena in some degree, and it is generally supposed that the hourly average of shooting stars is from five to ten, taking the whole year round. The matter composing these meteors we regard as identical with that ma.s.s of diffused atoms which forms a stratum conforming to the central plane of the vortex, and whose partial resistance to the radial stream occasions that luminosity which we call the zodial light. These atoms may coalesce into spherical aggregations, either as elastic gas, or as planetary dust, and, pa.s.sing outward on the radial stream, will occasionally become involved in the vortex of our own globe; and being drawn inwards by the polar current, and acted on by the earth"s gravity, be impelled with great velocity through the rarefied air of the upper atmosphere. That meteors are more abundant about the time of meridian pa.s.sage of a vortex (or, perhaps, more correctly speaking, from six to twelve hours afterwards, when the current of restoration penetrates the atmosphere), well accords with the author"s observations. It is about this time that high winds may be looked for, according to the theory; and it has ever been a popular opinion, that these meteors are a sign of windy weather. Even in Virgil"s time, the same belief prevailed, as a pa.s.sage in his Georgics would seem to indicate.
"Sape etiam stellas, vento impendente, videbis Praecipites clo labi; noctisque per umbram Flammarum longos a tergo albescere tractus;"
Virgil was a close observer of nature, and commences a storm with the wind at south, "Quo signo caderent Austri;" just as we have represented the usual course when these vortices pa.s.s near the observer"s lat.i.tude.
It is also a well-known fact, that after a display of meteors, (and we are now speaking of ordinary displays, and not of the great showers,) the temperature falls considerably. It is not uncommon also, that meteors are more abundant during an auroral display, as they ought to be by the theory. We must, however, exempt from this influence those solid meteors which sometimes come into collision with the earth, and afterwards grace the cabinets of the curious. These bodies may be considered microscopic planets, moving in stated orbits with planetary velocity, and bear strongly on the explosive theory of Olbers, as fully detailed by Sir David Brewster.
It is a very remarkable fact, first noticed by Olbers, that no fossil meteoric stones have yet been discovered. If this fact be coupled with the hypothesis advanced by Olbers, in reference to the origin of the asteroidal group, we should have to date that tremendous catastrophe since the deposition of our tertiary formations, and therefore it might possibly be subsequent to the introduction of the present race into the world. May not some of the legendary myths of the ancient world as mystified by the Greeks, have for a foundation the disappearance of a former great planet from the system? The idea of the existence of seven planets is one of the oldest records of antiquity; but the earth of course would not be counted one, and therefore in after times, the sun was included to make up the number; just as the signs of the Zodiac have been explained in accordance with the seasons of far later times than we can possibly a.s.sign for the invention of this division of the heavens.
Let those who have the leisure, try how far the contraction and dilation of the asteroidal orbits, to some average mean distance, will restore them to a common intersection or node, as the point of divergence of the different fragments. The question is interesting in many of its aspects, and may yet be satisfactorily answered.
The composition of aerolites may also be taken as indications of the common origin and elementary texture of the planets, whether they are independently formed or have originally pertained to a former planet; for no hypothesis of telluric or selenic origin yet advanced, can stand against the weight of evidence against it. Their fragmentary character rather favors the views of Sir David Brewster, and when we consider that they have been revolving for thousands of years with planetary velocity, and in very eccentric orbits, through the ether of s.p.a.ce, continually scathed by the electric blast of the radial stream, their rounded angles, and black glossy crust of an apparently fused envelope, may be accounted for, without difficulty, from the non-vitrified appearance of the interior. The composition of aerolites as far as known, embrace nearly one-third of all known simple substances according to Humboldt, and are as follows: iron, nickel, cobalt, manganese, chromium, copper, a.r.s.enic, zinc, potash, soda, sulphur, phosphorus, and carbon.
The theory we have thus given of the common occurrence of shooting stars, will render a satisfactory general account of their sporadic appearance; but there are other phenomena of greater interest, viz.: the occasional recurrence of swarms of such meteors, which defy all numerical estimates, being more like a fiery rain than anything they can be compared to. The most interesting feature of this phenomena, is the _apparent_ periodicity of their return. In the following table we have set down the most remarkable epochs mentioned by Humboldt, (and no man has devoted more attention to the subject,) as worthy of notice:
About April 22 to 25 " July 17 to 26 " August 9 to 11 " November 12 to 14 " November 27 to 29 " December 6 to 12
Besides these, he mentions two showers, from Arabian authority, in October; one in October, observed in Bohemia; one observed by himself, in the Pacific, on March 15; one February 4, just preceding the terrible earthquake of Riobamba, in 1797. The Chinese annals also contain many showers of stars, before the present era commenced. Some were in March, more in July, and others in different months. How, then, in view of these numerous dates, can we attach so much importance to the periodicity of these showers? The great shower of 1833, in the United States, on the 12th and 13th of November, brought to mind the great shower at c.u.mana, observed by Humboldt and Bonpland just thirty-three years before, to a day; and it must be confessed that more than ordinary displays have been seen on this date. Yet, on the strength of this, every meteoric shower is supposed to be periodical, and has resulted in a theory which becomes more complicated as the phenomenon is more observed, and can never lead to any useful and practical results. To cite the numerous instances of discrepant results, would only enc.u.mber this brief notice with facts neither interesting to the general reader, nor convincing to those who hold a contrary opinion. The author of these pages has watched for many years, and, in view of all the facts, has concluded that the doctrine of periodicity (as held by present meteorologists) is not tenable. The celebrated August shower failed, also, this year, at least in this place, as for four hours each night, on the 9th, 10th, and 11th, there were fewer bright meteors than at the close of July.
Professor Olmsted, who has paid considerable attention to the subject, has indeed attempted to connect the great November shower with the zodial light, which last he considers a nebulous body, of an elongated form, whose external portions, at this time of the year, lie across the earth"s path. (See Silliman"s Journal for 1837, vol. x.x.xiii. No. 2, p. 392.) He even gives its periods, (about six months,) the aphelion of the orbit being near the earth"s...o...b..t, and the perihelion within Mercury"s. In this way he attempts to explain both phenomena; but as the zodial light is seen unchanged all the year round in tropical lat.i.tudes, it is not the kind of body supposed by Olmsted, and the theory adds nothing to our knowledge. Others have imagined rings of nebulous matter, in which all the separate parts are moving in the same orbit around the sun, with a retrograde motion, and this, with some modifications, is the current theory of the day. The princ.i.p.al arguments rested on, for the support of this view, are derived from the great shower of 1833, in which a common radiant point was observed, and confirmed subsequently by the radiant of other years, in the same month of November. As this point is almost tangential to the earth"s...o...b..t at this season, the earth meets the nebulous ring moving in the contrary direction, and thus confers on these meteors the necessary velocity that is thought to be demanded by observation.
Now, our theory gives a totally different explanation of the phenomenon.
We contend that a retrograde motion of such a nebulous ma.s.s, is subversive of our whole theory; and we must be permitted to examine certain points, hitherto disregarded by those entertaining antagonist views. It is supposed that the meteors in 1833 fell for eight or nine hours. The orbital velocity of the earth is more than 1,000 miles per minute, and the orbital velocity of the nebulous zone must have had a similar velocity. During the nine hours of meteoric display, therefore, the earth traversed 500,000 miles of her orbit, which would give 1,000,000 miles for the depth of the nebulous stratum. But if of such vast extent, how happened it that the only part of the earth in which these were visible in great density, was the United States, or a s.p.a.ce embraced between the lat.i.tudes of 50 and 20 north, and the longitudes 60 and 100 west, (and these are the widest limits,) comprising only 1/40 of the surface of the globe? To a calm inquirer, this difficulty seems insurmountable. The author was then in the Mediterranean, on deck the greatest part of the night,--the weather fine, and nothing unusual visible in the heavens; from other sources he has also derived similar information. Yet, were the earth then pa.s.sing through a stratum of meteors 1,000,000 miles in extent, it is utterly inconceivable that other portions of the earth escaped. Much stress is also laid on the fact that these meteors in 1833, pa.s.sed from east to west generally, as they ought to do, if tangential to the earth in her orbit; but on the same phenomenon occurring in 1799, when the earth was in precisely the same part of her orbit, Humboldt says distinctly, "the direction (of the meteors) was very regular from north to south." How could this possibly happen, and at the same time be moving tangentially to the orbit?
There is also another fact of importance not duly weighed in forming such a theory. In 1833 the meteors evidently differed in velocity; one cla.s.s, consisting of luminous points, pa.s.sed like a shower of fire with great velocity to the westward, another cla.s.s were like large fire-b.a.l.l.s with luminous trains moving with less rapidity, while a third cla.s.s consisted of nebulous patches which remained stationary for a long time, and frequently emitting large streams of light. These last, at least, do not deport themselves as planetary bodies moving 2,000 miles per minute.
But the fact still remains, that unusual displays have occurred about the 12th and 14th of November; and also as a general thing when there are no unusual displays, the meteors are more abundant about this time.
Let us try if we can reconcile these facts with the theory of vortices.
We will first confine our remarks to the increased number of meteors about November 12th and 14th. The cosmical matter composing the zodial light, or at least the lighter parts of it, is continually driven outwards by the radial stream, just as the matter of a comet"s tail is stripped from the nucleus. This matter becomes involved in the terral vortex by descending the poles, and is again pa.s.sed out along the equatorial plane. The form of the zodial light, as seen edgewise, gives a lenticular form for the stratum of planetary particles composing it, and its central plane has been considered as coinciding with the plane of the sun"s equator. At the orbit of the earth, this lenticular s.p.a.ce is narrowed to a very thin stratum, but undoubtedly reaches beyond the earth"s...o...b..t with a rapidly diminishing density. As the axis of the sun is inclined about 7 to the ecliptic, and the ascending node is in the 20th degree of Gemini, the earth can only pa.s.s through the plane of the sun"s equator about the 12th of December and the 12th of June. If, therefore, the central plane of the vortex coincides with the plane of the sun"s equator, meteors ought to be more numerous about the dates above mentioned. But the observed times are on November 12th and 13th.
Now, from actual measurements, a computation has been made by M.
Houzeau, that the elements of the zodial light are materially different from those of the sun"s equator. He fixes the node of the light (according to Mr. Hind) in 2 heliocentric longitude, subject to an uncertainty of 12 or 13, and its inclination to the plane of the ecliptic, 3 35", subject to an uncertainty of about 2. The truth is, astronomers have argued the coincidence of the two planes from considerations connecting the zodial light with the sun"s equator, as if it were a solar atmosphere; but such an atmosphere is impossible, and it is high time such measures should be taken as will lead to some certain conclusion. If in the present state of the question, we were to take the mean, we should find the node in about longitude 40, which is the position of the earth on November 2d. But in the absence of measurements, we will a.s.sume, for the sake of argument, that the ascending node of the central plane of the vortex was, in 1833, in 50 heliocentric longitude, and consequently the earth was pa.s.sing through the meteoric stratum or central plane of the zodial light, on the night of November 12th. The opposite period of the year is May 12th--a date, it is true, on which no great shower of stars is recorded, but sporadic meteors are very plentiful at that time, and what is more important to observe is, that the 11th, 12th, and 13th of May, are the three noted _cold days_ which we have before mentioned. Thus truly indicating that the earth is then in or near the central plane of the vortex along which the radial stream is at its maximum of power at any given distance from the axis.
But the question occurs, does the node of this plane remain stationary, and is there no variation of the inclination of the axis of the solar vortex? We have found from observation, that the axis of the terral vortex is continually oscillating about a mean position by the action of the moon; and reasoning from this a.n.a.logy, and the constant tendency of a material vortex to preserve a dynamical balance, the same tendency must obtain in the solar vortex under the action of the great planets, whose orbits do not coincide with the central plane of the vortex. The ascending node of Jupiter"s...o...b..t is in longitude 98, Saturn"s 112, Ura.n.u.s" 72, Neptune"s 131; so that this plane does not correspond with the plane of greatest inertia discovered by La Place, and from the non-coincidence of these planes with the central plane of the vortex, must produce the same oscillation in the axis of the solar vortex, as the moon does in the terral vortex, but to what amount, observation can alone determine. Jupiter and Saturn will of course exert the greatest influence, and when these two planets are in conjunction, the ascending node of the central plane of the vortex will vary in longitude perhaps sufficiently to bring the meteoric maximum at the ascending node into October on the one hand, and to the close of November on the other, and at the descending node to April 25th on the one hand, and the close of May on the other.
The great showers of stars which have been recorded, must be therefore considered as an accidental exaggeration of a perennial phenomenon, attaining its maximum when the earth pa.s.ses through the central plane of the vortex, whose ascending node in 1833 we will suppose was in longitude 50. This theory will therefore account for those great showers which have occurred about the 24th of April, as well as those occurring in October and November; for it is far more consonant to all a.n.a.logy, to suppose the influx of planetary atoms into the solar vortex to be in irregular, than in regular quant.i.ties. Yet, whether in the one case or in the other, the matter will pa.s.s along the central plane of the vortex, either diffusely scattered or in denser clouds, and will be encountered by the earth when near the nodes _more frequently than at other times_. The phenomenon of 1833, may then be attributed to the earth encountering an unformed comet on the 12th of November; but we must reflect, that the medium of the vortex is also in motion, and the cometary matter drifting along with it; and that this motion corresponds with the earth"s motion. By becoming involved in the terral vortex, it will in a measure be carried along with the earth in her orbit as a temporary occupant of the terral vortex. But we are here met with the objection that the radiant being nearly stationary amongst the stars, demonstrated conclusively, that the source of these meteors did not partake of the earth"s motion. There is no difficulty in this. We suppose as a general thing, that the meteors descended to the surface of our atmosphere down the axis of the vortex (at least in the greatest numbers), and the geocentric longitude of this axis was nearly the same during the whole time of the display. We say nearly, for the motion of the moon in her orbit in nine hours, would change the longitude of the axis three or four degrees, and this is about the change in the position of the radiant noted at the time. This objection, therefore, falls to the ground; for the axis of the vortex, although carried along with the earth in her orbit, was unaffected by the earth"s rotation, and would therefore appear nearly as stationary in the heavens as Gamma Leonis. But it is again urged, that the moon was near conjunction with the sun, and consequently the central vortex was on the opposite side of the globe. This is true; but the outer vortex must have been near the meridian about three hours after midnight, or about the time when the radiant was vertical and the display the greatest. When the axis was to the eastward, the stars would shoot westward, when on the meridian, they would pa.s.s in all directions, but princ.i.p.ally to the south, on account of the inclination of the axis of the vortex; but this would only be true for places situated to the southward of the central lat.i.tude.
During the great shower of stars seen by Humboldt, in c.u.mana, the direction was to the south uniformly. Now, the lat.i.tude of c.u.mana is above 10 north, yet still too low for the general limits of the vortices; but from the same inclination of the axis (from 30 to 36 to the surface), the meteors would pa.s.s far south of the limit, and might even reach to the equator. The lat.i.tude of the _outer vortex ascending_ on November 12th, must have been near the line of greatest display, from the position of the moon at the time. We thus see why the phenomenon was limited to so small a fraction of the earth"s surface; why these meteors should be intermingled with nebulous patches stationary in the heavens for an hour together, and why, notwithstanding these facts, they were independent of the earth"s rotation.
We have yet another objection to answer, viz.: the planetary velocity of some of these bodies. Let us be understood. The velocity of a solid aerolite is due to gravitation, and is planetary, on the other hand, voluminous collections of cometary dust united by accident, and remaining so by mere inertia, are borne pa.s.sively on the ethereal currents with _electric_ velocity, and probably never penetrate far, even into the attenuated atmosphere, which may be supposed (from the facts connected with the aurora) to extend far above the denser stratum which refracts and reflects light, and from which the a.s.signed limits of our atmosphere have been derived.
It is generally considered that sporadic meteors are more numerous in the summer and autumn than in the winter and spring, and we have, likewise, in the tenth of August, a date which corresponds to many great displays and meteoric showers, both in recent and remote times. This would seem to vitiate our theory; for we cannot suppose that there are two _central_ planes in the vortex intersecting the ecliptic in longitude 320 and 50. We must remember, however, that as these great displays are accidental, and as the stratum composing the zodial light is manifestly of sufficient thickness to envelope the whole orbit of the earth, that it does not necessarily follow that the dense portions to which meteoric showers are due, should be always confined to the central plane of the vortex. And, besides, we have similar displays recorded in other months, which invalidates the theory of a regularly-recurring phenomenon. We shall, therefore, only aim at explaining why meteors are generally more abundant in summer and autumn than in the opposite seasons.
The axis of the solar vortex, considered as cylindrical, must be admitted to run out to a great depth on either side from the sun, and reach far into that unoccupied s.p.a.ce intervening between our system and the nearest fixed stars, and from these opposite points the solar vortex is supplied with that stream of ether which pa.s.ses down either pole to restore a partial equilibrium in the density of the ether of the vortex, rarefied by centrifugal force. As certain portions of the heavens are crowded with stars, and other parts comparatively vacant, we may expect a similar inequality in the distribution of that cometic dust, which causes a certain amount of extinction in the light of the stars, and, therefore, seeing that the two extremities of the axis of the solar vortex are so widely separated, it would not be wonderful if different quant.i.ties of such matter were brought down into the vortex from these extremities.
From recent observations made by H. R. Birt, at the observatory of the British a.s.sociation, it would appear that the brightest portion of the zodial light is always north of the ecliptic. Others have also remarked the same, and if we couple this fact with the suggestion just made, we are justified in suspecting that a greater quant.i.ty of cometic dust comes down the northern pole of the vortex than down the southern. This matter, in pa.s.sing outward, does not, of course, immediately attain to the central plane of the vortex, but is more thickly distributed along a plane parallel to this plane. And the same will be observed by that matter coming down the southern pole; it will be, in a certain degree, retained in a plane south of the central plane, but still parallel with it. This would account for the greater brightness of the northern side of the zodial light. It would, also, account for the greater frequency of meteors in summer and autumn than in the opposite seasons. From May to November the earth is above the central plane of the vortex, and, consequently, on the northern side; but after pa.s.sing the node in November, she is on the under or southern side, and the meteors are less frequent. With this general explanation we shall close. If what we have advanced be an approximation to the truth, the theory itself affords ample indications of what observations are requisite to prove or disprove it; and, on this account, a theory is of great benefit, as suggestive of many questions and combinations of facts which otherwise might never be thought of.
We have thus taken a cursory glance at the prominent physical phenomena of the world, and attempted to link them together in the bonds of one all-pervading principle. We have fearlessly taken a new path, and claim originality for the whole, disclaiming all intention of retailing second-hand wares, or of compiling an ingenious theory from heterogeneous sc.r.a.ps. If it be true, or if it be partially true, let those professionally engaged in such pursuits enter the wide field of investigation we have discovered for them; for if the whole theory be true, it only shows in a clearer light that the great work which has been fancied so near completion is scarcely yet begun; while the prospect of an ultimate and final completion of the temple which so many zealous votaries are erecting, is rendered mournfully hopeless by the contemplation of what yet remains to be performed.
FOOTNOTES:
[42] The orbit this year was determined under very unfavorable circ.u.mstances.
[43] According to other tables, this angle would be much greater than is given in Mr. Hind"s catalogue.
[44] Prin. Prop. xx Lib. Sec.
[45] With reference to the resisting power of the atoms.
[46] Prin. Lib. Tor. Prop, x.x.xix., also Prop, xli.