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quantity of invisible aqueous vapor that the spectroscopist can recognize the bands of this vapor in the planet's spectrum.

Even more perplexing is the circumstance that the cloud-masses should form themselves into zones. We can not get rid of this difficulty by a mere reference to the planet's rapid rotation, unless we are prepared to show how this rotation is to act in forcing the cloud-masses to become true belts. The whole substance of Jupiter and his whole atmosphere must take part in his rotation, and to suppose that aqueous vapor raised from his oceans would be left behind in the upper air like the steam from a railway engine, is to make a mistake resembling that which caused Tycho Brahé to deny the rotation of the earth, because bodies projected into the air are not left behind by the rotating earth. Nor is it conceivable that belts which vary remarkably, from time to time, in position and extent, should be formed by sun-raised clouds in the Jovian atmosphere, if the planet's surface is divided into permanent lands and seas.

But we are thus led to consider a circumstance which, as it appears to us, disposes finally of the idea that in the cloudrings of Jupiter we have to deal with phenomena resembling those presented by our own earth.

We are too apt in studying the celestial objects to forget that where all seems at nearly perfect rest, there may be processes of the utmost activity,-nay, rather of the utmost violence,-taking place as it were under our very eyes, and yet not perceptible save to the eye of reason. Looking at Jupiter, under his ordinary aspect, even in the finest telescope, one would feel certain that a general calm prevailed over his mighty globe. The steadfast equatorial ring, and the straight and sharply defined bands over either hemisphere, suggest certainly no idea of violent action. And when some feature in a belt is seen to change slowly in figure, or rather, when at the end of a certain time it is found to have so changed, for no eye can follow such changes as they proceed,-we are not prepared to recognize in the process the evidence of disturbances compared with which the fiercest hurricanes that have ever raged on earth are as mere summer zephyrs.

Indeed the planet Jupiter has been selected even by astronomers of repute as an

abode of pleasantness, a sort of paradise among the planet-worlds. There exists, we are told, in that distant world, a perennial spring, "A striking display of the beneficence of the Creator," says Admiral Smyth; "for the Jovian year contains twelve mundane years; and if there were a proportionate length of winter, that cold season would be three of the earthly years in length and tend to the destruction of vegetable life."

Even those who have denied that Jupiter can be the abode of life, and have formed altogether unfavorable ideas of his condition, have pictured him nevertheless as the scene of continual calm, though the calm is, according to their view, the calm of gloom and desolation. They recognize in Jupiter an eternal winter rather than a perpetual spring. Whewell, for example, in that once famous work the Plurality of Worlds, maintained that if living creatures exist at all in Jupiter, they must be wretched gelatinous monsters, languidly floating about in icy seas. According to him Jupiter is but a great globe of ice and water with perhaps a cindery nucleus, a glacial planet, with no more vitality in it than an iceberg.

But when we begin to examine the records of observers, and to consider them with due reference to the vast proportions of the planet, we recognize the fact that whatever may be Jupiter's unfitness to be the abode of life, it is not of an excess of stillness that his inhabitants (if he have any) can justly make complaint. Setting aside the enormous activity of which the mere existence of the belts affords evidence, and even regarding such phenomena as the formation of a disappearance of a new belt in two or three hours as merely indicative of heavy rainfalls or of the condensation of large masses of invisible aqueous vapor into clouds, there have been signs on more occasions than one, of Jovian hurricanes blowing persistently for several weeks together at a rate compared with which the velocity of our fiercest tornadoes seems utterly insignificant. During the year 1860, a rift in one of the Jovian cloud-belts behaved in such a way as to demonstrate the startling fact that a hurricane was raging over an extent of Jovian territory equalling the whole surface of our earth, at a rate of fully 150 miles per hour. It is not too much to say that a hurricane of like velocity on our earth would destroy

1872.]

A GIANT PLANET.

every building in the territory over which it raged, would uproot the mightiest forest trees, and would cause in fact universal desolation. At sea no ship that man ever made could withstand the fury of such a storm for a single minute. And yet this tremendous Jovian hurricane continued to rage with unabated fury for at least six weeks, or for fully one hundred Jovian days.

But during the last two or three years a change of so remarkable a nature has passed over Jupiter as to imply the existtence of forces even more energetic than those at work in producing atmospheric changes.

In the autumn of 1870, Mr. Browning (the eminent optician and observer) called the attention of astronomers to the fact that the great equatorial zone, usually, as we have said, of a creamy white color, had assumed a decidedly orange tint. At the same time it had become much less uniform in outline and sundry peculiarities in its appearance could be recognized, which have been severally compared to port-holes, pipe-bowls and stems, oval moldings, and other objects of an uncelestial nature. Without entering into descriptions which could only be rendered intelligible by means of a series of elaborate illustrations, let it suffice to say that the bright edges of the belts bordering on this ruddy equatorial zone seemed to be frayed and torn like the edges of storm clouds, and that the knots and projections thus formed often extended so far upon the great orange zone, from both sides, as almost to break it up into separate parts.

Now without inquiring into the particular form of action to which these remarkable changes were due, we can see at once that they implied processes of extreme energy. For, every one of the projections and knots, the seeming frayed edges of narrow cloud-streaks, had, in reality, an extent exceeding the largest of our terrestrial countries. Yet their aspect, and indeed the whole aspect of the ruddy belt, whose extent far exceeded the whole surface of our earth, changed obviously from night to night.

Strangely enough, these interesting observations, though they were presently confirmed by several well-known students of the heavens, did not attract that full attention from the senior astronomers of the day which they appear

ed to merit. Several, indeed, of our lead-
ing astronomers were disposed to deny
that any thing unusual was in progress,
based this opinion on a careful re-examin-
though none asserted definitely that they
ation of the planet's face. But quite re-
cently one of the most eminent of our
modern observers,-Mr. Lassell, lately
ciety (having been led to observe the
president of the Royal Astronomical So-
planet by the fact that certain phenomena
of interest in connection with the satellite
system are now in progress,) found his at-
tention attracted by the marvelous beauty
After describing the appearances he had
of the colors presented by Jupiter's belts.
intended to observe in the first instance,
he proceeds, "But this was not the phe-
rare and exquisite view of Jupiter. I must
nomenon which struck me most in this
acknowledge that I have hitherto been
inclined to think that there might be some
exaggeration of the colored views I have
lately seen of the planet; but this proper-
ty of the disk, in the view I am describing,
was so unmistakable that my skepticism is
statement be thought to express more
at last beginning to yield." Nor will this
than the truth, when we add that in the
picture accompanying his paper, Mr. Las-
sell presented the equatorial zone as brown-
as purple; one of the interinediate light
orange, and three neighboring dark zones
belts being pictured as of a light olive-
green.

Let us compare these observations made
in our brumous latitudes, with those ef-
equatorial of the Roman Observatory.
fected by Father Secchi with the fine
66 During the fine evenings of this month,'
The equato-
sented a wonderful aspect.
he wrote last February, "Jupiter has pre-
rial band, of a very pronounced rose color,
was strewn with a large number of yellow-
there were many very fine zones, with oth-
ish clouds. Above and below this band,
ers strongly marked and narrow, which re-
sembled stretched threads. The blue and
The
trast with the red zone, a contrast doubt-
yellow colors formed a remarkable con-
surface of the planet is actually so differ-
less increased by a little illusion.
ent from that which I have formerly seen,
that there is room for the study of the
planet's meteorology."

It appears to us that when these remarkable changes are considered in combination with the circumstance that on d

priori grounds we should expect the sun to have very little influence on the condition of the planet's atmosphere, the idea can not but be suggested that the chief source of all this energy resides in the planet itself. The idea may seem startling at a first view, but when once entertained, many arguments will be found to present themselves in its favor.

For instance, it does not seem to have been noticed, heretofore, as a very remarkable circumstance if the Jovian belts are sun-raised, that they pass round to the nocturnal half of Jupiter and reappear again, with the same general features as before, and this often for weeks at a stretch. Even that remarkable feature whose changes led to the conclusion that mighty hurricanes were in progress, yet changed continuously and regularly dur. ing the Jovian nights as well as during the Jovian days, for one hundred such days in succession. This is perfectly intelligible if the seat of disturbance is in the planet itself, but it is perfectly inexplicable, (as it seems to us,) if the sun occasions all these meteorological changes in Jupiter, as he occasions all the changes which take place in our earth's atmosphere. The alternation of day and night, which is one of the most potent of all the circumstances affecting the earth's meteorological condition, appears to have no effect whatever on the condition of Jupiter's atmosphere!

Now, as respects the alternation of summer and winter, we can form no satisfactory opinion in Jupiter's case, because he has no seasons worth mentioning. For instance, in latitudes on Jupiter corresponding to our own, the difference between extreme winter and extreme summer corresponds to the difference between the warmth on March 12th and March 28th, or between the warmth on September 15 and on September 31st. Yet we are not without evidence as to seasonal meteorological effects in the case of the sun's outer family of planets. Saturn, a belted planet like Jupiter, and in all other respects resembling him so far as telescopic study can be trusted, has seasons even more markedly contrasted than those on our own earth. We see now one pole now another bowed toward us, and his equatorial zone is curved now downward now upward, so as to form two half ovals, (at these opposite seasons,) which, taken together, would make an ellipse about

half as broad as it is long. As no less than fourteen years and a half separate the Saturnian summer and winter, we might fairly expect that the sun's action would have time to exert itself. In particular, we might fairly expect the great equatorial zone to be displaced; for our terrestrial zone of calms or "doldrums" travels north and south of the equator as the sun shifts northward and southward of the celestial equator, accomplishing in this way a range of no less than 3000 miles. But the Saturnian equatorial zone is not displaced at all during the long Saturnian year. It remains always persistently equatorial! Nothing could be more easy than the detection of its change of place if it followed the sun; yet no observer has ever suspected the slightest degree of systematic change corresponding with the changes of the Saturnian seasons. Or rather, it is absolutely certain that no such change takes place.

It appears, then, that night and day. and summer and winter, are alike withou influence on the Jovian and Saturnian cloud zones. Can it reasonably be questioned that, this being the case, we must look for the origin of the cloud zones in these planets themselves, and not in the solar orb, whose action must needs be largely influenced by the alternation of night and day and of the seasons?

But further, we find that a circumstance which had seemed perplexing when we compared the Jovian belts with terrestrial trade-wind zones, finds an explanation at once when we regard the belts as due to some form of action exerted by the planet itself. For let us suppose that streams of vapor are poured upwards to vast heights and with great velocity from the true surface of the planet. Then such streams starting from the surface with the rotational movement there prevailing, would be carried to regions where (owing to increase of distance from the centre) the movement due to the planet's rotation would be greater. They would thus be caught by the more swiftly-moving upper air and carried forwards, the modus operandi being the reverse of that observed when an engine leaves a trail of condensed steam behind it; or rather it may be compared to what would take place if a steam-engine were moving in the same direction as the wind but less swiftly, so that steam-clouds would be carried in front instead of behind.

Now, heat is the only form of force which could account for the formation of the enormous masses of cloud suspended in the atmosphere of Jupiter. And it seems difficult to conceive that the clouds could be maintained at a great height above the real surface of the planet unless that surface were intensely hot,-as hot perhaps as red-hot iron. If we supposed this to be the case we should find at once an explanation of the ruddy aspect of the dark belts. Nor would the change of the great equatorial belt from white to red imply more than that, owing to some .unknown cause, clouds had not formed during the last two years over the planet's equatorial zone, or, having formed, had been dispersed in some way. We need not even imagine a complete dispersion, since the best telescopes, and notably Mr. Buckingham's fine 21-inch refractor, have shown always a multitude of minute cloudlike objects over the ruddy equatorial zone. But the idea of a red-hot planet, or of a planet partially red-hot, will appear at a

first view too bizarre to be entertained even for a moment. We have been so accustomed to regard Jupiter and Saturn as other worlds, that the mind is disposed to reject the conception that they can be so intensely heated as to be utterly unfit to be the abode of living creatures.

This unwillingness to accept startling ideas is not to be altogether reprehended, since it prevents the mind from forming rash and baseless speculations. Yet we must not suffer this mental habitude, excellent though it may be in its proper place, to interfere with the admission of conclusions which seem based on trustworthy evidence. Let us then inquire whether the startling hypothesis to which we have been led by the study of observed facts may not be found to be in agreement with other facts not yet considered.

It will be obvious that if the real globe of Jupiter is thus intensely heated, a portion of the planet's light must be inherent. Therefore we might expect that the planet would shine somewhat more brightly than a globe of equal size and similarly placed, shining merely by reflecting the sun's light. Now two series of good observations have been made upon the luminosity of Jupiter. One was made by the late Professor Bond, of America, the other by Dr. Zöllner, of Germany. According to the former, Jupiter shines more brightly than he would NEW SERIES.-VOL. XVI., No. 1.

if he reflected the whole of the light falling upon him! According to the latter, and more trustworthy series, Jupiter does not indeed shine quite so brightly as Professor Bond supposed, but the planet yet shines three times as brightly as a globe of equal size would shine, if similarly placed, but constituted like Mars, and four times as brightly as such a globe would shine if constituted like our moon. Jupiter shines in fact very nearly as brightly as though he were constituted like one of our terrestrial clouds!

This result is highly significant. If Jupiter showed no belts and shone with a pure white color, we could explain it at once by simply regarding Jupiter as wholly cloud-covered or snow-covered (for snow and cloud shine with nearly equal lustre when similarly illuminated.) But the great dark belts which occupy so large a portion of the planet's disk altogether negative this supposition. We seem compelled to believe that some considerable portion of the planet's lustre is inherent.

Let us, however, proceed carefully here. We have to inquire first how far Zöllner's results can be trusted, and secondly, whether they are corroborated by any independent evidence. Now Zöllner carefully estimated the weight of his observations,-we may say he jealously estimated their weight, for it must be remembered that he was in no way interested in securing a greater or less result, while he was greatly interested in so stating the value of his results that those who might succeed him in the inquiry should not detect any serious error in his estimate. But his opinion of the probable degree of error in his observations was such as scarcely to affect to an appreciable extent the statements we have made above. Taking Zöllner's lowest estimate of Jupiter's brightness, that statement remains appreciably correct.

And next as to corroborative evidence. It happens that we have a very delicate means of measuring the degree of Jupiter's luminosity, as compared with that of other orbs similarly placed. For his satellites pass across his face, and nothing can be easier than to observe whether they appear darker or brighter than his surface.

It was an observation such as this which Mr. Lassell had made on the night when he noticed the ruddiness of Jupiter's great medial belt. By a singular chance Father Secchi made a similar observation during

his researches, and the reader will see, when we have quoted the narratives of both these observers, that the comparative darkness of all four satellites will have been established. "The fourth satellite," says Lassell, "has begun again for a season to cross the planet's disk, and I have looked out for opportunities of observing its passages, and was favored on the night of the 30th December last by witnessing a part of its passage under circumstances more than usually propitious. On its first entrance it was scarcely to be distinguished from the edge, not appearing at all as the others do, as a round bright spot. As it advanced it grew gradually manifestly darker than the surface of the planet, and by the time it had advanced a fourth of the way across it had become a very dark if not a black spot-so dark, indeed, that if I had looked at Jupiter without knowing any thing of the positions of his satellites, I should have said that a shadow (of a satellite) was passing. I remember having seen the like phenomenon many years ago; but my impression is that I had never seen the disk of the satellite so near to absolute blackness before. Of course it is only by contrast that it can possibly so appear; and we have in this fact a striking proof of the exceeding_brilliancy of the surface of the planet. In the same way the solar spots, if not surrounded by the marvelous splendor of the sun's surface, would doubtless appear as brilliant objects."

Next let us hear Secchi's account. "On the evening of February 3d," he says, "I observed the transit of the third satellite and that of its shadow. The satellite seemed almost black when it was upon the middle of the planet's disk, and notably smaller than its shadow, which was visible at the same time; one would have estimated it at only one-half. In approaching the edge the satellite disappeared, and reappeared soon after, close by the edge, but as a bright point. This fact is not a new one for the other satellites, but for the third it is unique. This result shows also the great difference of luminosity at the centre and near the edge of the planet, a difference already confirmed by photography."

It is hardly necessary to point out how strikingly these facts illustrate and confirm Dr. Zöllner's observations. But they also supply fresh evidence of a very interesting

nature.

Although a part of the difference dwelt on in Secchi's closing words may be ascribed to the oblique incidence of the light near the planet's edge, yet it does not appear to us that the whole difference can be thus explained. A difference so great that a satellite appears as a bright point close by the planet's edge, and almost black near the middle of the disk, suggests that the light near the edge is not reinforced by the inherent luminosity of our theory, that luminosity adding only to the brightness of the central parts of the disk. We would not insist too strongly on this inference, because the darkening due to oblique incidence is, under certain circumstances, very obvious to direct observation. But it seems to us that a portion of the difference should be referred to the inherent luminosity of the central parts of the disk. This being admitted, it would follow that the real solid globe of the planet is much smaller than the globe measured by astronomers; and that, therefore, instead of that amazingly small density which is so perplexing a feature of the planet's physical condition, Jupiter's globe may have a density equaling or exceeding that of the earth.

And after all, let us remember that the theory that Jupiter is an intensely heated globe-a theory to which we have been led by the consideration of many observed facts, and which in its turn suggests very satisfactory explanations of other observed facts-would merely show that, as Jupiter and Saturn hold an intermediate position between the sun and the minor planets in respect of size, so those giant orbs hold a corresponding position in respect of inherent heat. Roughly speaking, the earth is 8000 miles, the sun 840,000 miles, in diameter, and Jupiter, with his diameter of 82,000 miles, comes midway between these orbs. Now, the sun is at a white heat, and the earth gives out only what is called obscure heat; and if Jupiter's globe is at a red heat, he again comes midway between the sun and the earth.

We should be led by the theory here maintained to regard the major planets. which travel outside the zone of asteroids as in a sense secondary suns. So viewed, they could not be regarded as orbs fit for the support of living creatures. Yet, as each of them is the centre of a scheme of dependent worlds, of dimensions large

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