Of course, all of us learn geography and history. We must know the geography of the leading countries of the globe, and we must have some knowledge of their inhabitants and of their government, their resources and their civilization. It would seem shockingly ignorant not to know something about China, or not to have some ideas on the subject of India or Egypt. The discovery of the New World also involves matters on which every boy and girl has to be instructed. Supposing we were so far acquainted with the other globes scattered through space that we were able to gain some adequate knowledge of their geography and natural history, of the creatures that inhabit them, of their different products and climates, then everybody would be anxious to learn those particulars; and even when the novelty had worn off, it would still be right for us to know something about countries perhaps more populous than China, about nations more opulent than our own, about battles mightier than Waterloo, about animals and plants far stranger than any we have ever dreamt of. An outline of all such matters should, of course, be learned, and as the amount of information would be rather extensive, we will try to condense it as much as possible.
To aid us in realizing the full magnificence of that scheme in the heavens of which we form a part, I shall venture to give an illustration. Let us attempt to form some slight conception of the number and of the bulk of the books which would be necessary for conveying an adequate description of that marvellous universe of stars which surround us. These stars being suns, and many of them being brighter and larger than our own sun, it is but reasonable to presume that they may be attended by planetary systems. I do not say that we have any right to infer that such systems are like ours. It is not improbable that many of the suns around us have a much poorer retinue than that which dignifies our sun. On the other hand, it is just as likely that many of these other suns may be the centres of systems far more brilliant and interesting, with far greater diversity of structure, with far more intensity and variety of life and intelligence than are found in the system of which we form a part. It is only reasonable for us to suppose that, as our earth is an average planet, so our sun is an average star both in size and in the importance of its attendants. We may take the number of stars in the sky at about one hundred millions; and thus we see that the books which are to contain a description of the entire universe—or rather, I should say, of the entire universe that we see—must describe 100,000,000 times as much as is contained in our single system. Of course, we know next to nothing of what the books should contain; but we can form some conjecture of the number of those books, and this is the notion to which I now ask your attention.
So vast is the field of knowledge that has to be traversed, that we should be obliged to compress our descriptions into the narrowest compass. We begin with a description of our earth, for nearly all the books in the libraries that exist at this moment are devoted to subjects connected with this earth. They include various branches of history, innumerable languages and literatures and religions, everything relating to life on this globe, to its history in past geological times, to its geography, to its politics, to every variety of manufacture and agriculture, and all the innumerable matters which concern our earth’s inhabitants, past and present. But this tremendous body of knowledge must be much condensed before it would be small enough to retire to its just position in the great celestial library. I can only allow to the earth one volume of about 500 pages. Everything that has to be said about our earth must be packed within this compass. All terrestrial languages, histories, and sciences that cannot be included between its covers can find no other place on our shelves. I cannot spare any more room. Our celestial library will be big enough, as you shall presently see. I am claiming a good deal for our earth when I regard it as one of the most important bodies in the solar system. Of course it is not the biggest—very far from it; but it seems as if the big planets and the sun were not likely to be inhabited, so that if we allow one other volume to the rest of the solar system, it will perhaps be sufficient, though it must be admitted that Venus, of which we know next to nothing, except that it is as large as the earth, may also be quite as full of life and interest. Mars and Mercury are also among the planets with possible inhabitants. We are, therefore, restricting the importance of the solar system as much as possible, perhaps even too much, by allowing it two. Within those two volumes every conceivable thing about the entire solar system—sun, planets (great and small), moons, comets, and meteors—must be included, or else it would not be represented at all in the great celestial library.
We shall deal on similar principles with the other systems through space. Each of the 100,000,000 stars will have two volumes allotted to it. Within the two volumes devoted to each star we must compress our description of the body itself and of the system which surrounds it; the planets, their inhabitants, histories, arts, sciences, and all other information. I am not, remember, discussing the contents, but only the number of books we should have to read ere we could obtain even the merest outline of the true magnificence of the heavens. Let us try to form some estimate as to the kind of library that would be required to accommodate 200,000,000 volumes. I suppose a long straight hall, so lofty that there could be fifty shelves of books on each side. As you enter you look on the right hand and on the left, and you see it packed from floor to ceiling with volumes. We have arranged them according to the constellations. All the shelves in one part contain the volumes relating to the worlds in the Great Bear, while upon the other side may repose ranks upon ranks of volumes relating to the constellation of Orion.
I shall suppose that the volumes are each about an inch and a half thick, and as there are fifty shelves on each side, you will easily see that for each foot of its length the hall will accommodate 800 books. We can make a little calculation as to the length of this library, which, as we walk down through it, stretches out before us in a majestic corridor, with books, books everywhere. Let us continue our stroll, and as we pass by we find the shelves on both sides packed with their thousands of volumes; and we walk on and on, and still see no end to the vista that ever opens before us. In fact, no building that was ever yet constructed would hold this stupendous library. Let the hall begin on the furthest outskirts of the west of London, carry it through the heart of the city, and away to the utmost limits of the east—not a half of the entire books could be accommodated. The mighty corridor would have to be fifty miles long, and to be packed from floor to ceiling with fifty shelves of books on each side, if it is to contain even this very inadequate description of the contents of the visible universe. Imagine the solemn feelings with which we should enter such a library, could it be created by some miracle! As we took down one of the volumes, with what mysterious awe should we open it, and read therein of some vast world which eye had never seen! There we might learn strange problems in philosophy, astonishing developments in natural history; with what breathless interest we should read of inhabitants of an organization utterly unknown to our merely terrestrial experience! Notwithstanding the vast size of the library, the description of each globe would have to be very scanty. Thus, for instance, in the single book which referred to the earth I suppose a little chapter might be spared to an island called England, and possibly a page or so to its capital, London. Similarly meagre would have to be the accounts of the other bodies in the universe; and yet, for this most inadequate of abstracts, a library fifty miles long, and lined closely with fifty shelves of books on each side, would be required!
Methuselah lived, we are told, nine hundred and sixty-nine years; but even if he had attained his thousandth birthday he would have had to read about 300 of these books through every day of his life before he accomplished the task of learning even the merest outline about the contents of space.
If, indeed, we were to have a competent knowledge of all these other globes, of all their countries, their geographies, their nations, their climates, their plants, their animals, their sciences, languages, arts and literatures, it is not a volume, or a score of volumes, that would be required, but thousands of books would have to be devoted to the description of each world alone, just as thousands of volumes have been devoted to the affairs of this earth without exhausting the subjects of interest it presents. Hundreds of thousands of libraries, each as large as the British Museum, would not contain all that should be written, were we to have anything like a detailed description of the universe which we see. I specially emphasize the words just written, and I do so because the grandest thought of all, and that thought with which I conclude, brings before us the overwhelming extent of the unseen universe. Our telescopes can, no doubt, carry our vision to an immeasurable distance into the depths of space. But there are, doubtless, stars beyond the reach of our mightiest telescopes. There are stars so remote that they cannot record themselves on the most sensitive of photographic plates.
On the blackboard I draw a little circle with a piece of chalk. I think of our earth as the centre, and this circle will mark for us the limit to which our greatest telescopes can sound. Every star which we see, or which the photographic plate sees, lies within this circle; but, are there no stars outside? It is true that we can never see them, but it is impossible to believe that space is utterly void and empty where it lies beyond the view of our telescopes. Are we to say that inside this circle stars, worlds, nebulæ, and clusters are crowded, and that outside there is nothing? Everything teaches us that this is not so. We occasionally gain accession to our power by adding perhaps an inch to the diameter of our object-glass, or by erecting a telescope in an improved situation on a lofty mountain peak, or by procuring a photographic plate of increased sensibility. It thus happens that we are enabled to extend our vision a little further and to make this circle a little larger, and thus to add a little more to the known inside which has been won from the unknown outside. Whenever this is done we invariably find that the new region thus conquered is also densely filled with stars, with clusters, and with nebulæ; it is thus unreasonable to doubt that the rest of space also contains untold myriads of objects, even though they may never, by any conceivable improvement in our instruments, be brought within the range of our observation. Reflect that this circle is comparatively small with respect to the space outside. It occupied but a small spot on this blackboard, the blackboard itself occupies only a small part of the end of the theatre, while the end of the theatre is an area very small compared with that of London, of England, of the world, of the solar system, of the actual distance of the stars. In a similar way the region of space which is open to our inspection is an inconceivably small portion of the entire extent of space. The unknown outside is so much larger than the known inside, it is impossible to express the proportion. I write down unity in this corner and a cipher after it to make ten, and six ciphers again to make ten millions, and again, six ciphers more to make ten billions; but I might write six more, ay, I might cover the whole of this blackboard with ciphers, and even then I should not have got a number big enough to express how greatly the extent of the space we cannot see exceeds that of the space we see. If, therefore, we admit the fact, which no reasonable person can doubt, that this outside, this unknown, this unreachable and, to us, invisible space does really contain worlds and systems as does this small portion of space in which we happen to be placed—then, indeed, we shall begin truly to comprehend the majesty of the universe. What figures are to express the myriads of stars that should form a suitable population for a space inconceivably greater than that which contains 100,000,000 stars? But our imagination will extend still further. It brings before us these myriads of unseen stars with their associated worlds, it leads us to think that these worlds may be full to the brim with interests as great as those which exist on our world. When we remember that, for an adequate description of the worlds which we can see, one hundred thousand libraries, each greater than any library on earth, would be utterly insufficient, what conception are we to form when we now learn that even this would only amount to a description of an inconceivably small fragment of the entire universe?
Let us conceive that omniscience granted to us an adequate revelation of the ample glories of the heavens, both in that universe which we do see and in that infinitely greater universe which we do not see. Let a full inventory be made of all those innumerable worlds, with descriptions of their features and accounts of their inhabitants and their civilizations, their geology and their natural history, and all the boundless points of interest of every kind which a world in the sense in which we understand it does most naturally possess. Let those things be written every one, then may we say that were this whole earth of ours covered with vast buildings, lined from floor to ceiling with book-shelves—were every one of these shelves stored full with volumes, yet, even then this library would be inadequate to receive the books that would be necessary to contain a description of the glories of the sidereal heavens.