God's glory in the heavens/The Moon's Invisible Side
Plato.
III.
THE MOON'S INVISIBLE SIDE.
An artistic eye can readily discover, amidst much diversity, the pervading style of a great master. The architect may display his skill in very varied forms. The private dwelling, the public sanctuary, and the monumental pile may all reveal the genius of one presiding mind. There may be the utmost diversity of purpose, combined with a perfect unity of style. In the universe of worlds, it is not necessary to detect a sameness of purpose, in order to recognise the hand of the one great Architect. We do not require to prove that the moon is inhabited, in order to shew that it was formed by the same hand that constructed our world, teeming with living beings. Standing on the summit of a lunar mountain, and surveying the lifeless waste around, we can have no difficulty in tracing the same Divine wisdom that so marvellously moulded this world of ours, as a fit abode for all the activities of life. We find the same great laws that have sway upon our globe. Gravitation reigns there, as well as here. The forces that upheaved the crust of the moon, and moulded it into such strange forms, obeyed similar laws.
The configuration of the lunar surface bears a striking resemblance to the diversities on that of the earth. There are differences, but differences that consist with the same type. The solitary peaks, the mountain ranges, the circular craters have their own distinctive characters,—just as the scenery of one part of the earth's surface differs from that of another; still, there is one general plan assimilating them to the analogous terrestrial forms. It is this that gives so great a charm to the contemplation of the lunar surface. The pleasure of travel in foreign countries consists, very much, in the discovery of likeness to our manners and customs, arts and institutions, underlying much apparent and often startling dissimilarity; and when we travel beyond the limits of our own orb, and alight upon this strange island floating in space, we are startled to find it so strange, and yet so like the world that we left behind.
This pleasing similarity may be felt, and the hand of the one omnipotent Architect may be recognised, although we do not find the moon provided with inhabitants. Still it would, no doubt, lend an additional charm, if we had any plausible ground for entertaining such a belief. As soon as the telescope unveiled a world so like our own, in its general aspect, the popular imagination peopled it with living forms, and astronomers strove with one another to gratify the popular wish. On the dark surface, active volcanoes were discovered. The flames were seen to burst forth with great fierceness, and then slowly expire, shewing that there was air to sustain the combustion. Planets and fixed stars were seen to linger on the moon's edge, before they passed behind its disc, just as they ought to do, if there was an atmosphere. All these observations are now discredited; and the inexorable decision of scientific research is, that there is no valid argument for the existence of an atmosphere. Not long ago, an admirable test was afforded by the occultation of Jupiter, and every astronomer was on the alert to discover the result. The figure of the planet ought to be distorted by the atmosphere, if there was really one, and many eyes were strained to detect the distortion. The result was a strange one. Many saw the exact appearance that ought to be presented; the disc of Jupiter was changed just as theory required. Others again saw no distortion; the disc presented its natural form, and gave no indication of a refracting medium. What deduction are we to draw from such conflicting testimony? Where does the truth lie? The observers were all equally veracious, and they all appealed to the testimony of the senses. Which testimony are we to receive? Or must we hold that the evidence of the one side neutralises that of the other? The objective facts were undoubtedly the same to all; but a curious subjective law of our nature extricates us from the dilemma. The law is that of expectant attention, which explains so many of the facts of mesmerism. When the mind is possessed of some dominant idea, and when, in accordance with it, we have a strong expectation of some event, the senses, in these circumstances, become to a certain extent the sport of our subjective feelings. Taking this fact in our nature into account, and also the known character of the observers, the conclusion is, that the distortion of the disc of Jupiter was not real,—that it resulted merely from the excited state of the observers' feelings at the moment. Their foregone conclusion overpowered the legitimate testimony of sense. The testimony of the most competent observers was all against the existence of an atmosphere.
The advocates of a plurality of worlds have either abandoned the case of the moon as not one in point, being only a satellite, or resorted to strained hypotheses; such as, that there may be an atmosphere at the bottom of the valleys, or that she must necessarily have appropriated, by her attraction, the matter of the tails of comets, and of the zodiacal light. A recent discovery, has, however, been made, which entirely changes the aspect of the question. In all previous speculations, astronomers proceeded on the supposition that w^hat held in reference to one side of the moon, would equally hold in reference to the other. The profound research of a continental astronomer has now shewn, that this is by no means a legitimate supposition, and that the non-existence of an atmosphere in the visible side, does not, at all, imply that the other is equally destitute.
The moon constantly turns the same side to us. She does, indeed, as if to tantalise us, shew a small portion of the other side. She turns round at one time the western edge, so as to shew us a few more mountains and craters, and then, at another, the eastern; there is a similar oscillation at the poles, but it is only a very limited region that she thus reveals. It is by this libration, as we have seen, that we are able to take stereoscopic pictures of her disc. She turns constantly the same side to us, for the simple reason, that she rotates once upon her axis, in the same time that she performs a revolution round the earth. It, at first sight, appears like a contradiction, to say that she turns round upon her axis, and yet, that she never shews us but one hemisphere. Does not rotation consist in turning round to us all sides in succession? This has always been a puzzle in astronomy, though only very elementary knowledge is sufficient to solve it. Even the acute metaphysician Hegel could not understand how she should rotate, and he proves, from the fundamental principles of his philosophy, that she cannot. The perplexity arises from the position we occupy. If we were without, instead of within the circle she describes in the heavens, there could be no misconception. The inhabitants of the other planets see, in succession, all parts of her circumference. In the course of twenty-eight days they can scrutinise every part of her surface. For the same reason, a person, in the centre of a circus, sees only one side of the horse galloping round the circumference, while the spectators beyond see both sides in succession.
Until lately, no conjecture could be formed of the state of things on the other side of the moon. It was regarded as one of those inscrutable mysteries which it would be folly to attempt to unveil. Human genius has triumphed over the difficulty, and has thrown a curious light on that which has hitherto been involved in deepest darkness. And, in such cases, one feels at a loss which to admire most—the wonders of God's works, or the genius with which He has endowed man to explore these works. It is to M. Hansen that the credit of the discovery is due. Mr Airy, the Astronomer-Royal, supplied him, no doubt, with the data, but the merit of the solution is all his own. The Astronomer-Royal has, as it were, dug up from some Assyrian mound, a tablet with mystic cuneiform characters, and M. Hansen has supplied the key to the interpretation. The moon is so eagerly scrutinised at Greenwich, that any deviation from the prescribed path is soon detected. M. Hansen had already, on more than one occasion, vindicated the law of gravitation, by reducing unexplained lunar irregularities to its dominion. When again applied to, he set to work to discover the cause of the irregularity. The deviation was slight, but if the moon does not keep time to a very second, some explanation is required; and, on this, as on all former occasions, M. Hansen was triumphant. He has given a most marvellous solution, but one in which all astronomers have acquiesced.
The scientific statement of the solution is, that the moon's centre of gravity and her centre of figure are not coincident, the one being distant about 37 miles from the other. Most momentous results flow from this. The one hemisphere must be lighter than the other. This, indeed, is but another way of stating the discovery. The sphere of the moon may be regarded as made up of a light half and a heavy one—the lighter being always turned towards the earth.
But how could such a strange discovery be made? It would not be easy to give a popular explanation of the mathematical process by which M. Hansen arrived at this result, but there is no difficulty in understanding the general principles on which it is founded. In discharging a ball from a gun, calculation can predict che trajectory it will describe. But if the ball is not equally dense on opposite sides, it will not pursue the same path it would do if homogeneous. Let us suppose, that while the ball is perfectly spherical, one half is iron and the other cork, the curve described will be different, both in range and form, from that which would be described by a ball equally dense throughout. Balls have been, indeed, purposely so cast, to increase the range—the sphere being hollow, but having one side thicker than the other. Given the difference of density, the curve can be laid down, and given the curve, the difference of density can be determined. This last case is that of the moon. It differs in no respect from a ball discharged from a gun, and, in examining the curve it describes, the conclusion is, that while she is quite or nearly spherical, the hemisphere, turned towards us, is lighter than the opposite one.
But how does this tell on the question of inhabitants? The application is very direct and startling. Supposing the sphere of the moon originally covered with water, and enveloped in an atmosphere, both water and air would flow to the heavier side, and leave the lighter side destitute of both, just as water and air leave the summits of our mountains, and gravitate towards the valleys. They seek the lowest level, or, in other words, the point least distant from the centre of gravity.
In the case of the moon, the side turned to us is virtually one enormous mountain, and the opposite side the corresponding valley. We could not expect to find traces of air on the summit of a terrestrial mountain 134 miles high. The conclusion, therefore, is, that though the near hemisphere is a lifeless desert, having neither water nor air to sustain life, the hidden hemisphere may have a teeming population, rejoicing in all the comforts and amenities of life. The imagination is set free to picture broad oceans, bearing on their bosom the commerce of this new world, rivers fertilising the valleys through which they flow, a luxuriant vegetation, and buildings of colossal size.
This, however, only increases the mystery, and the longing to see farther round the limb of the moon. If there was mystery before, when life was not dreamt of, how much is that mystery increased, when we now know that there may be life—that there may be another world the counterpart of our own! Everything on this side of the moon, is fixed in the rigidity of death. No movement, indicating life or action, is observed. How different would be the other side, were we only permitted to obtain a glimpse! Its ever-changing atmosphere would be a source of continual interest. We could study its weather, as easily as our own; and, if the atmosphere was not too dense, we could watch the progress of agriculture, and the growth of cities. If it is a world of strife, we could distinguish, on the battle-field, the colour of the uniforms of the opposing masses. All this could be accomplished by our present optical means; and, as our powers of vision increased, we could descend to the minuter details of life. We could readily conceive a code of signals by which telegraphic communication might be carried on between us and our lunar neighbours. The moon, however, sternly withholds from us her great secret, and for ever turns from us her hidden hemisphere.
Granting that the other side of the moon is peopled, can our world be ever known to the inhabitants, seeing that only the lighter side is turned toward us? It is plain that the inhabitants, if they keep to their own side, can never get a glimpse of the earth. If there is an atmosphere, it is probable that it may extend a small way within the visible side, though in a rarefied form. We can then conceive the intrepid lunar inhabitants venturing, as far as they can breathe, within the barren hemisphere; just like adventurous travellers on our globe, scaling lofty mountains, to obtain an extended view of the landscape. What an astonishing spectacle must burst upon the view of the lunar tourist, as soon as he fairly gets within the new hemisphere! The traveller, who has spent the night on the summit of the Rigi, to watch the rising of the sun over the snow-clad ranges of the Oberland Alps, feels rewarded for all his toil by the glorious spectacle. The explorer of the southern hemisphere, when he first beholds the southern cross and the Magellanic clouds, experiences no ordinary delight at having ushered into view a new portion of God's universe. But these illustrations can, but imperfectly, enable us to realise the case of the lunar traveller, when he first beholds the earth. He will see an immense blue orb hung up, immovably fixed, in the heavens. It will appear to him fourteen times larger than the moon appears to us. The sun will be seen, as in the other lunar hemisphere, to rise in one horizon, and in fourteen days set, in the opposite; but the earth never moves. The stars at midday, as well as at midnight, will appear to pass behind its disc, while it maintains the same position. But though immovably fixed in the heavens, wondrous activities will be discovered. It will exhibit in twenty-eight days all the phases of the moon — now a thin crescent, then a full orb. Its rapid rotation will, also, be a most notable object, for, in so large an orb, the twenty-four-hours' period will be most marked. And then the blue atmosphere will be undergoing incessant changes. Belts, corresponding to the trade-winds, will be seen, and throughout the whole extent, the varying climates of the world will be observable. Though objects on the surface of the earth will be but dimly descried, still our seas, continents, and mountain-ranges may be distinguished. What a tale of wonder will the traveller have to tell, when, after his perilous adventures, he returns to the bosom of his family!
It is obvious, that the results of M. Hansen furnish no positive evidence for the existence of lunar inhabitants. It is valuable to the advocate of a plurality of worlds, only in as far as it enables him to rebut the argument of his antagonist, when he points to the moon as a proof that his speculations are only a dream. He can now maintain, that if we knew all, we would find that the moon is not destitute of life.
While we write (1860), tidings are brought of the discovery of a new planet, and a new difficulty for the advocate of planetary inhabitants. Strange, that with so many professional eyes gazing day after day at the spots on the sun, it should be left to a provincial doctor in France, with the rudest instruments, to make the discovery of the little black pellet-like spot, which, by its form and rapid motion, indicated the transit of a new planet within the orbit of Mercury. The honour, after all, does not fall to the man of keen eyes, who detected this spot accidentally, but to the master-mind, who, by a finer sense, detected its existence, months before the results of observation were made known. Leverrier, in this case, as in that of the planet Neptune, was the intellectual seer.