Unfinished Worlds.

Te Aroha News, Volume VII, Issue 468, 3 May 1890, Page 3

Unfinished Worlds.

By Sir Robert Ball, Astronomer Royal for Ireland. By the term world we mean, usually speaking, the 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 development. We may represent our entbj for instance, as a world, in the maturity of its being, but there are others wtdoh 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. It is of these latter worlds that we are specially going bo speak in this paper. Suppose that you came into a room and found a pitcher of water on the table, you place your hand on the pitcher, and you feel that the water is 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 warm, and have grown cold, and you could nob 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 speaking in this paper. 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 do not doubt that it must have been much hotter when the blacksmith drew it from the fire than you have now 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, was 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 affect the reasoning. If you found the body to be heated 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 wo 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 that volcanoes pour forth show us that the earth is anything but cool in the lower reigns. Other terrestrial phenomena bear similar testimony. Hot springs, for instance, evince the heated condition of the deepseated 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 now referring to such _ heat as is produced by combustion. We are discussing the way in which a body which 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. Wc are not even able to estimate how many thousands of years have elapsed since man began his course on our globe, bub 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 which now grows. Time after time have these races of organised 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 nob 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 that 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 much 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 heab must have been even 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, car, if they be heated sufficiently high, be not only 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.

I hope I have made my arguments clear, bub if not let me use the following illustration. Suppose that a boy has brought pocket money with him to school, but that he receives none during the term. Every week this boy visits the pastry cook’s shop and buys and pays for a good share of the dainties he finds there. Supposing that he was able to do this even up. to the end of the term, it is at least certain that he must have had a handsome allowance to commence with. This is similar to the argument we have followed in discussing the cooling of the earth. We infer that the schoolboy had considerable money at the beginning of the term simply from the fact that without having had his resources replenished he is able to carry on a continuous expenditure. In precisely the same way we are entitled to conclude that in the beginning of things the earth must have been uncommonly rich in heat, as otherwise it could nob have sustained for all these ages that incessant loss of heat by ladiation which even at the present is in operation.

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 onr earth’s past history. I shall only mention one or two. The first that I may refer to is especially famous. It is the great nebula of Orion. Wo find in this constellation an object which is practically speaking invisible to the naked eye ; it has only the effect of producing a slight haziness in the stars which form the sword handle of Orion in the quaint fashion in which the constellation used formerly to be represented. When viewed through a telescope of sufficient pow-er, a most marvellous spectacle is disclosed. 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 selfluminous, 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 object terminates. Probably this nebula will in some remote age, gradually condense down into more solid substances. It contains, no doubt, enough material to make as 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 form bright sunlike bodies. .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 nebulas 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 in Orion. Such globes are doubtless undergoing condensation, and may be regarded as unfinished worlds. The End.