We must leave Sir David and Dr Lardner to settle their small amount of differences together; for Sir David will have it that “the moon exhibits such proofs of an atmosphere that we have a new ground from analogy for believing that she either has, or is in a state of preparation for receiving, inhabitants;”[[76]] whom, “with monuments of their hands,” he “hopes may be discovered with some magnificent telescope which may be constructed!”[[77]] And he is compelled to believe that “all the other unseen satellites of the solar system are homes to animal and intellectual life.”[[78]] The Essayist would seem not to have deemed it necessary to deprive the sun of inhabitants; but our confident Pluralist will not surrender the stupendous body so easily. His friend Dr Lardner properly regards it “as a vast globular furnace, the heat emitted from each square foot of which is seven times greater than the heat issuing from a square foot of the fiercest blast-furnace: to what agency the light and heat are due, no one can do more than conjecture. According to our hypothesis, it is a great Electric Light in the centre of the system;”[[79]] and “entirely removed from all analogy with the earth”—“utterly unsuited for the habitation of organised tribes.”[[80]] Nevertheless Sir David believes that “the sun is richly stored with inhabitants”—the probability “being doubtless greatly increased by the simple consideration of its enormous size”—a “domain so extensive, so blessed with perpetual light;” but it would seem that “if it be inhabited,” it is probably “occupied by the highest orders of intelligence!”[[81]] who, however, are allowed to enjoy their picturesque, and, it must be owned, somewhat peculiar, but doubtless blessed position, only by peeping every now and then through the sun’s spots, and so “seeing distinctly the planets and stars”—in fact, “large portions of the heavens!”[[82]] Perhaps it may be thought that this is not a very handsome way of dealing with such exalted beings!
The Essayist has now our seven principal sister-planets to deal with—the two infra-terrestrial, Mercury and Venus, and the five extra-terrestrial—Mars, Jupiter, Saturn, Uranus, and Neptune;—and as to all these, the question continues, do they so resemble the earth in physical conditions, as to lead us safely to the conclusion that they resemble it in that other capital particular, of being the habitations of intellectual and moral beings? Here, be it observed, that every symptom of unlikeness which the Essayist can detect, greatly augments the burthen of proof incumbent upon his opponents.
When it was discovered that the old planets in certain important particulars resembled the earth, being opaque and solid bodies, having similar motions round the sun and on their own axis, some accompanied by satellites, and all having arrangements producing day and night, summer and winter, who could help wondering whether they must not also have inhabitants, reckoning and regulating their lives and employments by days, months, and years? This was, at most, however, a mere guess or conjecture; and whether it is now more probable than then, depends on the intervening progress of astronomy and science in general. Have subsequent discoveries strengthened or impugned the validity of the conjecture? The limits of our system have been since vastly extended by the discovery of Uranus and Neptune; and the planetary sisterhood has also increased in number by thirty little and very eccentric ones.
Now, as to Neptune, says the Essayist, in substance, what reason has a sensible person for believing it peopled, as the earth is, by human beings—i. e. consisting of body and soul? He is thirty times further than we are from the sun, which will appear to it a mere star—about the size of Jupiter to us; and Neptune’s light and heat will be nine hundred times less than ours![[83]] If it, nevertheless, contain animal and intellectual life, we must try to conceive how they get on with such a modicum of those useful elements!
But have we general grounds for assuming all the planetary bodies inhabited? Beginning with the moon, we have encountered a decided negative. If any planet, however, have sufficient light, heat, clouds, winds, and a due adjustment of gravity, and the strength of the materials of which organisation consist, there may be life of some sort or other. Now we can measure and weigh the planets, exactly, by the law of gravitation, which embraces every particle of matter in our system, and find the mass of our earth to be only five times heavier than water. Comparing it with Jupiter—the bulk of which is 1331 times greater than that of the Earth—his density is, as a whole, only a quarter of that of the Earth—not greater than it would be as a sphere of water; and he is conjectured to be such, and the existence of his belts to be lines of clouds, fed with vapours raised by the sun’s action on such a watery sphere—the lines of such clouds being of so steady and determined a character, in consequence of his great rotatory velocity. Equal bulk for equal bulk, he is lighter than the Earth, but of course much heavier altogether; and as he is five times the Earth’s distance from the Sun, he must get a proportionally smaller amount of light and heat, and even that diminished by the clouds enveloping him to so great an extent. What a low degree of vitality, and what kind of organisation must animal existence possess, to suit such physical conditions, especially with reference to gravity, which, at his surface, is nearly two and a half times that on the Earth! Boneless, watery, pulpy inhabitants of the cold waters; or they may be frozen so far as to exclude the idea of animal existence; or it may be restricted to shallow parts in a planet of ice.[[84]] But if this be so, to what end his gorgeous array of satellites?—his four moons? “Precisely the same,” answers our pertinacious Essayist, “as the use of our moon during the countless ages before man was placed on the earth; while it was tenanted by corals, madrepores, shell-fish, belemnites, the cartilaginous fishes of the old red sandstone, or the Saurian monsters of the lias. With these differences, it is asked, what becomes of analogy—of resemblances justifying our belief that Jupiter is inhabited like ourselves?”
To this answers Sir David Brewster—Jupiter’s great size “is alone a proof that it must have been made for some grand and useful purpose:” it is flattened at its poles; revolves on its axis in nearly ten hours; has different climates and seasons; and is abundantly illuminated, in the short absence of the sun, by its four moons, giving him, in fact, “perpetual moonlight.” Why does the sun give it days, nights, and years? Why do its moons irradiate its continents and seas? Its equatorial breezes blow perpetually over its plains? To what purpose could such a gigantic world have been framed, unless to supply the wants, and minister to the happiness, of living beings? Still, it is admitted,[[85]] “that certain objections or difficulties naturally present themselves.” The distance of Jupiter from the sun precludes the possibility of sufficient light and heat from that quarter, to support either such vegetable or animal life as exists on the earth; the cold must be very intense—its rivers and seas must be tracks and fields of ice.[[86]] But it may be answered, that the temperature of a planet depends on other causes—the condition of its atmosphere, and the internal heat of its mass—as is the case with our earth; and such “may” be the case in Jupiter; and, “if” so, may secure a temperature sufficiently genial to sustain such animal and vegetable life as ours; yet, it is owned, it cannot “increase the feeble light which Jupiter derives from the sun; but an enlargement of the pupil of the eye, and increased sensibility of the retina, would make the sun’s light as brilliant to Jovians as to us.”[[87]] Besides, a brilliant phosphorescent light “may” be excited in the satellites by the sun’s rays. Again, the day of ten hours may be thought insufficient for physical repose; but, it is answered, five hours’ repose are sufficient for five of labour. “A difficulty of a more serious kind,[[88]] however, is presented by the great force of gravity on so gigantic a planet as Jupiter;” but Sir David gives us curious calculations to show that a Jovian’s weight would be only double that of a man on the earth.
Struck by such a formidable array of differences, when he was in quest of resemblances only,
“Alike, but, oh! how different!”
Sir David rebukes the sceptic for forming so low an opinion of Omnipotent Wisdom, as to assume that “the inhabitants of the planets must be either men, or anything resembling them;—is it,” he asks, “necessary that an immortal soul should be hung upon a skeleton of bone, or imprisoned in a cage of cartilage and skin? Must it see with two eyes, and hear with two ears, and touch with ten fingers, and rest on a duality of limbs? May it not rest in a Polyphemus with one eyeball, or in an Argus with a hundred? May it not reign in the giant forms of the Titans, and direct the hundred hands of Briareus?[[89]] The being of another world may have his home in subterranean cities, warmed by central fires; or in crystal caves, cooled by ocean tides; or he 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!”[[90]]
Let us pause at this point, and see how the question stands on the showing of the respectively imaginative and matter-of-fact disputants themselves. Sir David Brewster, being bound to show that analogy forces us to believe Jupiter inhabited, is compelled to admit a series of signal discrepancies in physical condition; expecting his opponent, in turn, to admit such a series of essential alterations, both of inert matter and organisation, as will admit of what?—totally different modes of animal and intellectual existence—so different, as to drive a philosopher into the fantastic dreams in which we have just seen him indulging. Not so the Essayist, a master of the Inductive Philosophy. He does not presume impiously to limit Omnipotence; but reverently owns His power to create whatever forms and conditions of existence He pleases. But when it is asserted that He has, in fact, made beings wholly different from any that we see, “he cannot believe this without further evidence.”[[91]] And on this very subject of the imaginary inhabitants of Jupiter, he says, after reading what his heated and fanciful opponent has advanced,—“You are hard,” he makes an objector say, “on our neighbours in Jupiter, when you will not allow them to be anything better than ‘boneless, watery, pulpy creatures.’” To which he answers, “I had no disposition to be hard on them when I entered upon these speculations. I drew, what appeared to me, probable conclusions from all the facts of the case. If the laws of attraction, of light, of heat, and the like, be the same there as they are here, which we believe to be certain, the laws of life must also be the same; and, if so, I can draw no other conclusions than those which I have stated.”[[92]]