# In the High Heavens/Chapter 2

CHAPTER II.
THE PHYSICAL CONDITION OF OTHER WORLDS.
Y the term world we mean, usually speaking, this globe on which we stand; but the merest glance at the sky through a telescope will show us that our world is only one of many worlds. Further reflection and study of other parts of the universe will convince us that among these other worlds there are many in different stages, so to speak, of their development. We may represent our earth, for instance, as a world in the maturity of its being, but there are others which exhibit different phases of progress. Some will appear as worlds which are to be regarded in extreme old age, while others again seem to be in an imperfect or immature condition.
Suppose that you came into a room and found a pitcher of water on the table. You placed your hand on the pitcher and you felt that the water was tepid. If you knew that the pitcher had stood there for an hour, you would be able to draw the conclusion that the water must ​have been hotter when it was placed there than when you felt it. If when you had felt the temperature you found the water as cold as the air in the room, then you could not infer its original temperature. It might have been a jug of cold water to begin with, or it might have been warm, and have grown cold; you could not tell which. If, however, the water be in the slightest degree warmer than the air in the room, then the argument that it must have cooled from a higher temperature is irresistible. This is so obvious a doctrine that it may seem unnecessary to write it down. But, obvious though it be, it will yet teach us much about the past history, both of our earth and of other globes; especially will it prove instructive about those unfinished worlds of which we are now speaking.
If in a blacksmith's forge you incautiously placed your hand upon a piece of iron, and it burned your fingers, and if the blacksmith told you that the iron had lain there for half an hour, you would not doubt that it must have been much hotter when the blacksmith drew it from the fire than you found it to be. Probably it was even red hot at the time it was laid aside. The argument would still apply if the object, instead of being a lump of iron, were a block of stone; it would apply if the body were as big as a mountain or as big as the moon; neither the fire nor the material would really affect the reasoning. If you found the body to be hot you may feel perfectly certain that hours ago, or days ago, or years ago, or centuries ago, it must have been hotter still. We must apply this argument to that immense globe, 8,000 miles in diameter, on which we are standing. It has an exterior crust of rocks and stones, ​and contains a good deal of iron inside. This great ball is undoubtedly very hot in its interior. We have many reasons for knowing this to be the case. The eruptions of volcanoes afford the simplest proof. The smoke, the ashes, and the molten lava which volcanoes pour forth show us that the earth is anything but cool in the lower regions. Other terrestrial phenomena bear similar testimony. Hot springs, for instance, evince the heated condition of the deep-seated rocks. Any miner will tell you that the deeper his mine the hotter he finds his work to be. The gain in heat arises from the fact that the deeper the mine the nearer it lies to the central incandescence. We are not now referring to such heat as is produced by combustion. We are discussing the way in which a body that has once been heated by a fire, or by some other agency, gradually parts with its heat and falls in temperature. There is no means of replenishing to any large extent the heat of the inside of our earth by combustion. The earth's interior temperature must, therefore, on the whole, be simply falling in accordance with the laws of cooling.
The conclusion to which we are led by this reasoning is a remarkable one. We know that our earth has been in existence for an incalculable period of time. We are not even able to estimate how many thousands of years have elapsed since man began his course on our globe, but the human period is merely the latest of all the great periods in world-history. Long before man commenced to live here the earth was the abode of life; countless races of animals, large and small, now generally extinct, roamed through forests of trees, or through vegetation of a kind largely if not wholly different from anything ​ Fig. 3.—Spiral form of the Nebula in Canes Venatici (Lord Rosse) ​which now grows. Time after time have these races of organized beings passed away and been replaced by others entirely different. There were times when this globe was inhabited by reptiles far larger than any terrestrial animals now living. All the zoological gardens in the world at present would not be nearly large enough to contain representative specimens of all the varieties of animals which have from time to time found a home on this earth. But these animals have now passed away, and the only means we have of learning that they ever existed is afforded by the occasional skeletons which in the form of fossils are now and then extracted from the rocks. No one has succeeded in making any reliable estimate of the number of years which have run their course since first this globe assumed its present shape. But no one can doubt that these years are to be reckoned in their millions, though whether these millions are to be expressed in units or tens or hundreds, or in periods even greater still, is a matter beyond our knowledge.
During all these ages the earth must gradually have been growing colder, and therefore at the beginning it must have been hotter than it is to-day. As we look back earlier and still earlier the earth ever seems hotter and hotter through the ages. At least the argument points to a time when the earth must have been hot even to its surface, so hot that you could not stand on it, and then earlier still it was red hot, white hot, and molten. Even here the argument does not fail; we find the heat must have been greater and greater the further we look back, until at last we come to a time when the now solid materials of our earth must have been in a widely different form. For we know that the most infusible materials ​like steel or flint can, if they be heated sufficiently high, not only be transformed into a liquid, but even be driven off into a vapour. Thus we learn that there was a time when our earth was merely a mass of glowing gas.
A great deal of light is thrown upon this subject by looking at other worlds, some of which are to be seen in quite an unfinished state even at the present moment. They are unfinished in the sense that the gaseous material has not yet condensed down sufficiently to form a solid globe. There are thousands of bodies with which astronomers are acquainted which will in one way or another illustrate these phases of our earth's past history. I shall only mention one, which is typical of a remarkable class of similar objects. Fig. 3 represents one of the famous spiral nebulæ, discovered many years ago by the late Earl of Rosse. The object is invisible to the naked eye. It seems like a haze surrounding the stars, which the telescope discloses in considerable numbers, as shown in the picture. When viewed through an instrument oi sufficient power a marvellous spectacle is revealed. There are wisps and patches of glowing cloud-like material which shine not as our clouds do by reflecting to us the sunlight. This celestial cloud is self-luminous; it is in fact composed of vapours so intensely heated that they glow with fervour. As I write, I have Lord Rosse's elaborate drawing of this nebula before me, and on the margin of this stupendous object the nebula fades away so tenderly that it is almost impossible to say where the luminosity terminates. Probably this nebula will in some remote age gradually condense down into more solid substances. It contains, no doubt, enough material to make many globes as big as our earth. Before, however, it ​settles down into dark bodies like the earth, it will have to pass through stages in which its condensing materials will form bright sun-like bodies.
Fig. 4.—Crab Nebula.
It seems as if this process of condensation might almost be witnessed at the present time in some parts of the great object.
There are also some very striking nebulæ which are often spoken of as planetary. They are literally balls of bluish-coloured gas or vapour, apparently more dense ​than that which forms the nebula now under consideration. Such globes are, doubtless, undergoing condensation, and may be regarded as incipient worlds.
Our fellow-planets like the earth are guided and held in their ever-circling way by the attraction of the sun, while they are also illuminated by the light which he pours forth with such liberality, and warmed with the rays of heat which he sends them. The sun does not, indeed, confer these benefits in an equal degree on all the members of his family; those which are nearer to him get much, perhaps too much according to our notions, of his heat, while those like Uranus or Neptune, which lie on the outskirts of the system, get little, perhaps too little, of those particular benefits which he dispenses. This world of ours thus occupies a somewhat intermediate position. The structure of the human body would have to be considerably modified if we were to find a congenial residence either so near the sun as Mercury or so far from him as Neptune. As we live on this earth in the temperate regions, and suffer neither from the fearful heat at the equator nor from the horrors of the frozen poles, so too does our entire world enjoy what we may describe as a temperate situation in the series of bodies belonging to the solar system.
In other respects, too, our position is an intermediate one. There are some planets, such as Mars and Mercury, which are very much smaller than our earth. There are other planets, such as Jupiter and Saturn, which are enormously greater than the earth; and there is Venus, our beautiful neighbour, which is almost exactly the same size. Considering that this earth may be taken as an average specimen of the worlds which form the sun's ​family, it is natural to inquire how far the other planets may be constituted in the same way as our own. Most of the questions which we should like to ask on this head are such as, unhappily, cannot be answered. Especially should we like to know whether the other planets are inhabited, but on this our greatest telescopes can give us no information whatever, and we can only form the vaguest surmises. The features that would be discernible on the neighbouring planets must be immense indeed. It would, for example, be utterly impossible for us to recognise towns, even if such objects as towns existed, though it might still be possible to discern the broader outlines of extensive continents or mighty oceans. We could also observe the clouds, if clouds existed, around a neighbouring planet, because owing to their extent and to their position on the outside they would be comparatively easy to see, while the incessant changes of the clouds would render them an attractive feature to the observer.
We have accordingly in this chapter decided to say what we can with respect to the clouds and oceans which are to be met with on some of the other planets. Even here, however, we must be content with a knowledge which is much more scanty than an intelligent curiosity would desire. In many of the planets we can see little or nothing of this kind that can be certainly made out, while even on those which we can see best it is only the very broadest and most striking features that can be discerned. Of Venus, unhappily, we can see nothing or next to nothing that would give us any information as to the presence or the absence of oceans and clouds. The loveliness of the evening star is due to the brilliancy of the sun-beams in which she is decked, ​but this very brilliancy is inconvenient in the telescope, where it merely appears as a glare which renders all details invisible.
Fig. 5.—Comparative Sizes of the Planets. The great circle represents the Sun.
Beyond a few ill-defined and inconspicuous marks, nothing has ever been seen on this planet which is of any interest for our present purpose. Though clouds are comparatively an unimportant feature on Mars, they assume the most extraordinary importance on Jupiter. He is a gigantic body, by far ​the largest of all the planets; larger, indeed, than all the other planets put together. Viewed in the telescope, the surface of Jupiter is usually seen crossed by two belts, one above and one below his equator. You would produce something like them on any ordinary globe by making a broad belt on the tropic of Cancer, and another on the tropic of Capricorn. Now, these belts on Jupiter are not fixed features of his surface; they are constantly changing their aspect. Sometimes they are hardly to be seen at all, and on other occasions they widen their limits and become irregular at their edges; the greater part of the surface of the planet is more or less covered over with similar markings. We see nothing on this great planet that resembles the oceans and continents on Mars, nor have we any indications of arctic regions on Jupiter's surface. In fact, the longer we look at Jupiter, the more we become convinced that the surface of the planet is swathed with a mighty volume of clouds so dense and so impenetrable that our most powerful telescopes have never yet been able to pierce through them down to the solid surface of the planet. Indeed we can hardly say whether this planet has any solid interior at all. There is one object on Jupiter known as "the great red spot," which for several years was more or less recognisable. This seemed to be a great volcano, or some other projection from beneath, which was tall enough and large enough to make itself visible through the mighty covering of clouds which act as an effectual screen to hide all objects of lower prominence.
There is another very interesting way in which we can confirm the fact that the apparent volume of Jupiter is swollen by these mighty clouds which so closely encase ​him. Careful measurements having been made it has been shown that Jupiter is 1,200 times bigger than our earth: in other words, that 1,200 globes, each as large as this earth, rolled together into one, would only form a ball as big as this mighty planet. Astronomers also have the means of weighing a great planet as well as of measuring it. How this weighing is to be effected I shall not here pause to describe; suffice it to say that the little moons by which Jupiter is attended afford by their movements the means of answering the question; and the answer is a significant one, for we find that Jupiter is about 300 times as heavy as the earth. This gives us, indeed, an impressive idea of the magnificence of the mightiest of the planets. Were a pair of gigantic weighing scales constructed, and Jupiter placed in one of these scales, then it would require 300 globes each as heavy as the earth to be placed in the other before the mighty balance could turn. Yet when we remember that Jupiter is 1,200 times as large as the earth we may well feel surprised at learning that he is only 300 times as heavy. Were the constitution of the planet at all like that of our earth, then the weights and the sizes should observe the same proportions, just as one solid iron ball, when ten times as big as another, will be ten times as heavy. The lightness of Jupiter in comparison with his size is really the point that merits our astonishment. He is, indeed, not so very much heavier than a globe of water the same size would be, while our earth is five times as heavy as a globe of water equally large. The true explanation is that Jupiter is so swollen by these enormous masses of cloud which surround him as to give him a bigness altogether out of proportion to his mass. Therefore, as Mars gives ​us an illustration of the existence of oceans on other planets, so Jupiter provides us with a splendid example of a planet encompassed with clouds.
It is interesting to compare the circumstances attending our residence on this earth with the corresponding conditions that would be found if we could change our abode from this globe to another planet. I propose to discuss a few of the points which arise when we consider such questions. In the first place we must remember that our bodies have been specially organized and adapted to suit our surroundings on this particular world. I do not think it is at all probable that a man could exist, even for five minutes, on any other planet or any other body in the universe. We know that within even the limits of our own earth, each one of us has to be provided with a constitution appropriate to a particular climate. An Eskimo is suitably placed in the arctic regions, a negro on the equator; and were they to change places, it is hard to say whether the heat would not have killed the Eskimo even before the cold killed the negro. But such an attempt at acclimatization would be easy when compared with that which would be required before an inhabitant adapted to one globe could accommodate himself to a residence on another. Indeed, there seem to be innumerable difficulties in supposing that there can be any residence for man, or for any beings nearly resembling man, elsewhere than on his own earth.
Let us specially review a few of the other globes, beginning with the sun. I think we need not give many reasons to show that a man could not live there long. Every boy knows how a burning glass can kindle a piece of paper by concentrating the sun's rays. Some great ​burning glasses have been constructed with which iron, steel, and even flints have been actually melted by the sun's heat. It can be proved that the sun himself must be hotter than any temperature that can be produced in the focus of the most powerful burning glass. We certainly cannot conceive any organized being which would find a congenial residence in a temperature vastly hotter than that of the most powerful furnace that has ever been known. Assuredly there can be no life on the sun.
Fig. 6.—The Clouds on Jupiter, October 14th, 1891.
The next celestial world in importance to the sun is, of course, the moon. Could we find here an eligible abode for mankind? The moon would, no doubt, provide the necessary alternation from day to night, but the day on ​the moon would last for a fortnight, and then there would be black night for another fortnight. During the long day the moon would be terribly scorched, a circumstance which would be hardly compensated for by the fact that even if we survived the scorching we should certainly be frozen to death during the ensuing night.
Fig. 7.—Jupiter, showing the shadow of a Satellite, October 15th, 1891.
But there would be other insuperable difficulties attending an attempt to make an abode on the moon. The absence of water is one of them, while a still more immediate trouble would arise from the deficiency, if not total absence, of air suitable for respiration. Indeed, it is almost impossible for us to conceive what an airless world would be like. Fishes out of water would not be more uncomfortable than we should ​find ourselves. But suppose that we managed to bring a supply of oxygen that might enable us to avoid suffocation by the use of artificial respiration, we should still find the moon a very strange world. We could hear nothing, for sound exists not except in air. We could strike no match or light no fire. We could feel no wind and see no clouds. There would be also an embarrassment of a different kind which there would not be any way of obviating.
Suppose that we were actually on the moon, and that we had in some way obtained the necessary provision both of air and of water, and had begun to walk about, we should experience sensations of a novel description. The extraordinary lightness of everything would be specially noticeable. Take a lump of iron which weighs six pounds on the earth, you would find on the moon that it seemed to weigh only as much as one pound would do on the earth. Everybody knows that it requires considerable exertion to lift a 56 lbs. weight here, but on the moon it would hardly require as much effort as you ordinarily have to put forth to lift ten pounds. Indeed, the weight of every object on the moon would be reduced to the sixth part of that which the same object has on the earth. No doubt in some ways this might prove a convenience to the moon dwellers, Their bodies would partake of the general buoyancy; walking and running would be amazingly facilitated; and the same effort that would enable you to jump over an obstacle three feet high here would carry you with ease over a wall eighteen feet high on the moon. A good cricketer can throw a ball about a hundred yards here. If he made the same exertion on the moon he could throw the ball over a third of ​a mile. The diminished gravitation would prove of service in athletic performances on the moon. Not only would a bicycle be driven along with unparalleled ease and rapidity if the lunar roads were smooth, but even the disagreeable process of taking a header over the handles would lose its terrors, for the lunar bicyclist would fall gently and softly to his mother earth. It may, however, be questioned whether our bodies would be adapted for a life under such conditions. It seems almost certain that as the muscular system of the human body has been arranged to work with the particular gravitation that is found on this earth, it would be impossible for it to be accommodated to a gravitation which had only a sixth of the intensity for which it was adapted. On these grounds we conclude that neither the times nor the seasons, neither the gravitation nor the other distinctive features of the moon, would permit it to be an endurable abode for life of the types we are acquainted with.
Let us now consider some of the more distant worlds, and examine their claims to be regarded as possible homes for beings in any degree resembling ourselves. There are many of these worlds with regard to which we may at once decide in the negative. Could we, for instance, live on a planet like Neptune? It lies thirty times as far from the sun as we do. The share of the light and heat from the sun which a Neptunian inhabitant would receive could only be the nine-hundredth part of that which is dispensed to every dweller on this earth. This fact alone would seem to show an insuperable obstacle to the existence of any life on Neptune resembling those types of life with which we are familiar. The orbit of ​Neptune is also so vast that the planet requires a period of 165 years in order to complete a single revolution. The changes of Neptunian seasons must, therefore, be extremely protracted. A man who was born at midwinter in Neptune would have reached extreme old age if he survived until the next ensuing mid-summer.
I cannot discuss the times and seasons of all the celestial bodies, so I have taken a few typical instances. Neptune was appropriate as being the most remote planet. Now let us speak of Jupiter, the greatest planet. The day and night on Jupiter are both extremely short, for together they do not quite amount to ten hours. Jupiter's year, however, is almost twelve of our years. Although a man on Jupiter would only receive one-twenty-fifth part of the heat of the sun that he would do on the earth, yet it does not seem likely that there would be reason to apprehend that Jupiter would be uninhabitable from cold. Quite the contrary is the case. Indeed, it seems not unlikely that the excessive heat of Jupiter would be found intolerable by beings with nerves like ours. This heat has, however, not come from the sun; it is the internal heat of the planet itself, which has not yet sufficiently cooled down from that original fiery condition characteristic of every body of our system in its initial stages.
Jupiter certainly has an atmosphere, but we do not know from what gases that atmosphere may have been blended. It might consist of materials noxious, if not actually poisonous; and in any case it is extremely unlikely that it should contain both the ingredients and the proportions suited to our organs of respiration. But there are independent grounds for knowing that Jupiter must be an impossible home for beings so constituted as we are. On ​the moon every object would be deprived of five-sixths of its weight, because the moon is a comparatively small globe. Were we, however, to be transferred to Jupiter, the weight of every object would receive an extraordinary augmentation. Our muscles would be found utterly inadequate to their work. Walking, or even standing, would involve the most fearful exertion, while rising from bed in the morning would be a difficult, indeed, probably, an impossible process. I see no likelihood that Jupiter can be the home of any life whatever.
We may dismiss from our present consideration such bodies as the comets. A comet moves during the greater part of its course through the depths of space at inconceivable distances from the sun. Out there, the comet traverses regions where the cold would be absolutely incompatible with life of any type conceivable by us. Then for a brief period, to be measured in months, weeks, days, or even hours, the comet is wheeling around the sun, where it is often exposed to a frightful temperature sufficient to fuse and even vapourise bars of wrought iron. A comet, indeed, is not a likely abode for life, though I ought to mention that comets often contain the element carbon. This is a very singular fact when it is remembered that carbon is one of the substances essentially associated with life in the forms in which we know it.
There is, however, one body in our system whose times and whose seasons accord so closely with our own that it is impossible not to believe that life of some kind may there be found. The length of the day and night together on Mars is 24 hours 37 minutes; that is practically only about half an hour greater than the corresponding period for our own globe. The year of Mars is, no doubt ​longer than ours, being about a year and eleven months. The size of Mars is less than the size of our earth, and, therefore, the gravitation on Mars is not so great as we have here. I do not mean to say that it is the least likely that any man, woman, or child transplanted from this earth to Mars could live and thrive there. The temperature might be endurable, and water appears to be not wanting, but I do not think we have any reason to expect that the atmosphere would suit human beings either in quantity or quality. As, however, the case of Mars will be discussed in another chapter in this volume, we do not here refer to it further.