  WHY PARLEY BELIEVES THAT THERE IS A GREAT SOURCE OF HEAT WITHIN THE GLOBE. If you have attended to what I have already told you, you will have seen that there must be a close connection between the causes of volcanoes, earthquakes, and hot springs, (if they are not all to be ascribed to one cause,) from their always occurring in the neighbourhood of each other. But there is something else that you ought to notice in reference to this connection. I said, that a volcanic eruption was almost always preceded by shakings of the ground round the root of the mountain. These shakings are sometimes so violent as to be dreadful earthquakes, There was once a great earthquake which kept on for some days on the north shore of South America, and then stopped quite suddenly. It was afterwards found out, that just at the moment it stopped, a tremendous eruption burst forth from a volcano in one of the West-India islands, more than 150 miles off. You know what the safety-valve of a steam-engine is. Now it would seem just as if volcanoes were safety-valves for the power which causes earthquakes. Very well.—I am now going to tell you what people have thought this power has been owing to. Before I do so, that you may not be disappointed, I should tell you that we know very little on the subject; nor shall we ever know much till somebody can get down to the centre of the earth, unless some of the little black spirits, that the Rosicrucians called Gnomes, and fabled to live in the middle of the globe, should In the meantime, we can only guess; but we ought to guess as well as we can, and see whether our guess is not much more likely to be true than any of the others. Volcanic bands are always near the sea-shore, and it has therefore been generally supposed that water has something to do with their action. If you take a mixture of sulphur and iron filings, and mix them into a paste with water, and then bury them in the ground, after a while they will become hot and send out a great quantity of steam. Some people have imagined that this is the way in which volcanic activity is produced, but no one thinks so now, and for very good reasons, for there is nothing in the action so produced at all capable of accounting for long continued eruptions, or for the flowing out of the lava. Sir Humphrey Davy found out, that nearly all Sir Humphrey thought he had got the true explanation of the thing. These wonderful metals formed the basis of every substance in lava, and supposing them to exist in the centre of the globe, it was only necessary for water to get to them to set them on fire, and thus to give rise to earthquakes and volcanoes. It appeared only to be required that a crack should be made at But you would find it very difficult to think how this can account for continual and nearly steady operations, such as have been known to exist in the Geysers of Iceland for more than 1000 years, and in Mount Stromboli for much longer than that, so we will try another guess. It has been observed in descending deep mines, that the earth gets warmer the deeper you go. The usual mode of trying it is to dig little holes, as you go down, in the sides and bottom of the mine, and put a thermometer into them. A great many observations of this kind, have been made in different parts of the world, and the greatest care has been taken to allow for all causes of irregularity, consisting A similar conclusion has been drawn from the heat of the water of the Artesian Wells. But, perhaps, you do not know what Artesian Wells are, so I will tell you. They are deep borings in the earth, out of which water rises to, or even above, the surface of the ground. Wherever you bore, if you go deep enough you may get plenty of water, and this water is always found to be warmer in proportion to the depth of the well in which it rises. They are called Artesian Wells, from Artois, a town in France, where the first was constructed. In a well of this kind near Rochelle, which was 316 feet deep, the water near the surface was at a temperature of 55 degrees, and at the bottom 60 degrees. It was afterwards sunk to Do you not think it most likely that the heat continues to increase quite as fast in proportion below the deepest point that man has gone down to? Well, if so, at the depth of some miles it must be hot enough to melt anything, even granite, and all kinds of stones. If we suppose, on this evidence, that the centre of the globe is intensely heated, and that it gets gradually cooler towards the surface, there is what at once will account for the hot springs, the increasing heat in descending mines, the constant action of some volcanoes, the occasional action of others, the streams of lava, and the nature of all substances that are thrown out. It is very natural to imagine that every now and then the action of the great heated mass inside, would crack open the crust, and the sea wearing away its bottom in some places as it does, may have something to do in assisting this. Then, after a time, these cracks might be partially, or wholly, filled up by the matter thrown into them, and the volcanoes on the surface above may become quiet for a time. |
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