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trial men would be as active as they are, if his height were to theirs as one to two and a half. Hence, setting six feet as the maximum ordinary height of men on the earth, we see that the tallest and handsomest of the Jovicolæ can be but about two and a half feet in height, if only our premises are correct. Thus Tom Thumb and other little fellows, if removed to Jupiter, might be wondered at for their enormous height, and eagerly sought after by any Carlylian Fredericks who may be forming grenadier corps out yonder.
One line of argument having thus led us to regard the Jovi. cola as Ogs of Bashan, while another equally plausible has re. duced their dimensions to those of our two-year-old children, we may fairly conclude that this method of reasoning is fallacious. We must not measure the inhabitants of other worlds according to the conceptions suggested by the forms of life we are acquainted with upon earth. We must admit the possibility that arrangements as different from those we are familar with as the constitution of the insect is from that of man may be presented amid the orbs which circle round the sun. unwise, no doubt, to give free scope to speculation where we have, in truth, no means of forming an opinion. We need not imagine, as some have done, that “the inhabitants of Jupiter are bat-winged," or, with others, " that they are inveterate dancers.” Nor to take the views of more respectable authorities, need we agree with Sir Humphry Davy that the bodies of the Jovians are composed of “ numerous convolutions of tubes more analogous to the trunk of the elephant than anything else;" with Whewell, that they are pulpy, gelatinous creatures, living in a dismal world of water and ice with a cindery nucleus ; nor finally, with Brewster, that the Jovian may have his “home in subterranean cities warmed by central fires, or in crystal caves cooled by ocean tides, or may float with the Nereids upon the deep, or mount upon wings as eagles, or rise upon the pinions of the dove, that he may flee away and be at rest” (sic). So soon as we give a definite form to the conceptions that the imagination, free from the control of exact knowledge, frames respecting the inhabitants of other worlds, we touch at once on the grotesque, the hideous, or the ridiculous. It is sufficient to recognize the probability, or rather the certainty, that the beings of other worlds are very different from any we are acquainted with, without endeavoring to give shape and form to fancies that have no found ation in fact.
We may regard it as probable, however, thàt living creatures in Jupiter, if any exist, are built generally on a much smaller scale than those which people our earth. Trees, plants, and the vegetable world generally, must also, one would imagine, be very differently constituted from those we are familiar with. It is well known that the motion of the vegetable juices is in part regulated by the force of gravity, and therefore it must be admitted that the structure of terrestrial plants is in part dependent upon the value of gravitation at the earth's surface. Whewell, in his “ Bridgewater Treatise" on the astronomical evidence of design in creation, lays great stress on this relation, pointing out, if I remember aright, that all vegetation would be destroyed at once if there could suddenly take place any marked change in the earth's attractive forces. If this view is correct, it is certain that none of our plants could thrive on the soil of Jupiter.
The year of Jupiter differs in a much more striking manner than that of Mars from our terrestrial year. It consists of nearly twelve such years as ours, so that the period corresponding to one of our seasons lasts nearly three years, and a Jovian month is nearly equal to one of our terrestrial years. He has, however, no seasons in our sense of the word, since his equator is inclined but little more than three degrees to his orbit. Thus a perpetual spring reigns all over his surface.
But before we proceed to form a high opinion of the planet's condition under the influence of this perpetual spring, let us distinctly understand what the word means. The word “spring ” has a genial sound to ourselves, because we associate it with that which is commonly the pleasantest portion of our year; but it is just possible that the perpetual spring reigning over Jupiter, though doubtless well adapted to the wants of his inhabitants, leads to a state of things such as we might not find altogether so agrecable.
It has been said that" as the rays of the sun fall perpendicularly on the body of the planet, and always continue to do so, the heat must be nearly as possible equal at all times of the year, a perennial summer; this is a striking display of beneficent arrangement.” But we should be cautious in adopting this mode of argument. If Jupiter's great distance from the sun is compensated for by this peculiar disposition of his axis, and we are to admire the beneficence thus displayed, are we therefore to find maleficence in the fact that Saturn, Uranus, and Neptune have been otherwise dealt with, though, being further from the sun, they have greater need than Jupiter of some special arrangement of the sort? It seems safer to consider the consequences which flow from the arrangement without any special reference to its purpose, lest, in our over-anxiety to recognize beneficence in the treatment of one world, we should adopt a mode of reasoning which leads to the direct conclusion that other worlds have been ill-treated.
The great peculiarity resulting from the arrangement in question — the only peculiarity, in fact, of which we can speak with any confidence – consists in this, that everywhere on Jupiter day and night are of equal length. It is in this sense only that perpetual spring - or perpetual autumn, if we please -- reigns on the giant planet. The different latitudes of Jupiter have climates differing quite as much as those found in different latitudes on our own earth. At the equator the sun passes every day nearly to the point overhead. At the poles the sun seems to glide along the horizon, rising in the east, passing round always near the horizon — toward the south, and thence to his setting-place in the west. In intermediate latitudes the sun passes to a southerly elevation, which is greater or less according as the place is nearer to or further from Jupiter's equator, It follows that there is a marked difference between the subequatorial and the subpolar regions in Jupiter, while between these regions every intermediate climate is to be found.
Owing to the rapidity of Jupiter's rotation, the motion of the sun in the Jovian sky must be much more readily discernible and measurable than that with which the sun seems to pass across our own heavens. He traverses the whole semicircle, from the eastern to the western horizon, in two minutes less
an five hours, or about six degrees in ten minutes. This corresponds to a motion through a space equal to the sun's diameter (as we see him) in fifty seconds, and must be readily discernible, even to the unaided vision of the Jovicolæ, unless their eyesight is much inferior to ours. The smallness of the sun, as seen from Jupiter, must help to render the motion more perceptible. He presents to them an apparent diameter only equal to about one-fifth of that with which we see him, so that in ten seconds he seems to pass over a space equal to his own diameter.
The other celestial bodies are affected with similar motions as seen from Jupiter. Of course, those seen near the poles of his heavens seem relatively at rest. One of these poles lies in the heart of the constellation Draco; the other lies close by the Greater Magellanic Cloud, which must present a magnificent cynosure to the inhabitants of the southern hemisphere of the planet. The contrast between the steadfastness of the polar star-groups and the swift motions of the equatorial constellations must be impressive indeed. These equatorial groups are no other than our old friends the zodiacal constellations. As seen by the inhabitants of Jupiter, they rise with a perceptible but stately motion above the eastern horizon, pass to their culmination on the southern meridian, and so to their setting-place in the west — exhibiting the same splendors which the terrestrial astronomer delights to gaze upon, enhanced by the peculiar impressions of active power suggested by visible and obvious motion. It
may seem, at first sight, that the presence of the Jovian satellites must tend to dim the splendor of the sidereal heavens. Our own moon, despite the beautiful passage in which Homer has described the calm beauty of a moonlit night, certainly detracts largely from the magnificence of the star-groups; and as at times there must be four moons visible above the horizon of the Jovians, it might seem that all but the brighter stars would be quite obliterated. The first moon must appear somewhat larger than our own; the next has an apparent diameter rather more than half as large as that of our moon; the third (really the largest) appears about as large as the second; and the fourth has an apparent diameter equal to about a quarter of our moon's. Thus, in all, they cover a space on the sky more than half as large again as that which our moon covers. But, in reality, they cannot have nearly so marked an effect in dimming the lustre of the stars. For it must not be forgotten that they shine only by reflecting the sun's light, and that he illuminates them but faintly in comparison with the light he pours upon our own moon. In effect, supposing their reflective capacities equal to the moon's, they must appear less brilliant than she does, in the proportion of about one to twenty-five ; and, combining this result with the above relation, it follows that even if they could all be “ full” together, they could send to the Jovians but about one-sixteenth part of the light we receive from the full moon. But, as a matter of fact, they cannot all be full together. The motions of the inner three are so related that, though there is nothing to prevent them from being all visible together, yet when so visible, one only can be full. The fourth may be full at the same time, or in fact may be associated with the other three in any way, since its motions are not bound up with theirs as theirs are inter se.
Even now, however, we have not reached a full estimate of the extent of the mistake which those astronomers have made who speak of the splendor with which the satellites of Jupiter illuminate his skies. When at that part of their orbits where they would otherwise be full, the three inner moons are always eclipsed ; and though the fourth, by reason of its great distance, sometimes escapes eclipse, yet more frequently it is obscured like the others. The two inner satellites are eclipsed for upward of two hours, and as they occupy but a few hours in completing their circuit round the sky, it will be seen how largely this relation detracts from their light-supplying powers.
We see, then, that those writers have been mistaken who allege that the great distance of Jupiter from the sun is compensated by the number of his moons, and the quantity of light they reflect toward him. So far is this from being the case that, under the most favorable circumstances, they can supply during the Jovian night but about one-twentieth part of the light with which the full moon illuminates our nocturnal skies. The poetical descriptions which imaginative writers have indulged in, respecting the splendor of the scene presented by these satellites, will not bear the dry light of numerical estimation. That the satellite-system of Jupiter subserves, or may hereafter subserve, important functions need not be questioned ; but that we can recognize them as created for any special purpose may be assuredly denied.