Through the Earth/Chapter II
THE CENTRAL HEAT
"ES," repeated Mr. Curtis, bringing down his fist with a bang, "that 's where the real difficulty lies; that 's where the impossibility arises. The other obstacles might perhaps be overcome if sufficient time and money were devoted to the work. But the great question is, How will you manage when you reach the center of the earth, where the materials are one mass of liquid fire? Answer me that!"
"How do you know the earth is a mass of liquid fire at the center?" inquired the doctor, coolly.
"How do I know it? Why, all the best authorities concede the fact."
"Indeed, I was not aware of it. On the contrary, I thought that our most profound thinkers all rejected this theory."
"You mean to say that the center of the earth is not a mass of molten matter at a white heat?"
"We have every reason to believe that this is not the case."
"Then how do you explain that, in mines, the temperature becomes warmer the deeper down you go? You will at least admit this fact, will you not?"
"Certainly," said Dr. Giles; "that fact is well established. But you must remember that our deepest mines barely extend a couple of miles into the earth."
"Still, in those two miles the increase in heat is considerable, the bottom of the mine being always hotter than the top."
"True; but this increase varies considerably in different parts of the earth, being much less in some mines than in others."
"Yes; but the average increase, as I understand it, has been found to be about 1° F. for every sixty feet, so that, if we accept this as the normal rate, the heat at the depth of a very few miles would be sufficient to melt the hardest rocks we know of."
"That would be true enough," said the doctor, "if the heat continued increasing at the same rate. But this scarcely appears possible. You might as well claim that, because the temperature becomes colder the higher we ascend on a mountain, if we were to continue forever in a vertical line the temperature would keep on decreasing at the same rate."
"Well, would n't it?"
"Most certainly not. We, of course, know very little about the matter, but this we do know, that there is a point of absolute cold, which is supposed to be at 459° F. below zero. A body at this temperature would have absolutely no heat left in it. Our scientists may very well be mistaken as to the exact figure, but, at any rate, we know that there is some point beyond which the cold cannot continue to increase as we ascend in the air. Hence those who argue that because the cold becomes greater when we climb a mountain, it would continue increasing at the same rate if we ascended into the heavens, would be altogether mistaken. Similarly, those who claim that because the temperature becomes higher as we descend in mines, the heat must be inconceivable after we have gone a few miles, have no logical basis for their statement."
"But does not the existence of volcanoes prove that there is a central fire in the interior of the earth?"
"It proves that there are certain incandescent masses in the interior, but not that the whole center of the earth is in a molten condition. In fact, if the earth were liquid at the center, the incandescent matter, or sea of fire, would have tides just as our oceans of water have. Consequently every active volcano would have each day two high and two low tides, whereas nothing of the sort happens. Indeed, all the manifestations with which we are familiar accord more closely with the theory of a solid earth than of one containing a sea of molten matter."
"But how about earthquakes? Do not earthquakes occur continually in every portion of the globe? And are not these earthquakes caused by internal heat?"
"True; but the earthquakes only lend support to what I have said. It is an undeniable fact that the land in almost every country on the face of the earth is slowly but continually either rising or falling. These elevations and depressions are, however, so gradual that most persons do not even notice them; in fact, very delicate instruments are required to ascertain their occurrence. It is only when they are very sudden and very violent that the general public hears of them as the earthquakes which destroy houses, devastate forests, or engulf whole villages."
"Well," said Mr. Curtis, triumphantly, "it seems to me that these facts support what I have just said. Whether the earthquake be great or slight, it must be produced by the same causes; and since these earthquakes occur continually in all parts of the world, it must be because the interior of the earth is in a liquid state."
"Excuse me," said Dr. Giles; "but I was about to add that the subject of earthquakes has been very carefully studied by seismologists, and the best authorities have calculated that the origin of the disturbance is usually not very deep in the interior of the earth—probably not over thirty miles below the surface in the most violent earthquakes, and certainly at a much slighter depth than this in many cases. Now, if the whole interior of the earth were in a liquid state, it would be natural to expect that the origin of our earthquakes would be at a much greater depth."
"So far as you are concerned," remarked Mr. Curtis, "I don't see that it makes very much difference whether the whole interior of the earth is incandescent, or whether there are only small seas of liquid fire scattered around within thirty miles of the surface. In either case you must count on having to battle with the internal heat of the earth."
"Oh, certainly," said Dr. Giles; "I have arranged to do so."
"What!" exclaimed Mr. Curtis, astonished, "you mean to say that you could dig your tunnel through these seething lakes of fire?"
"That is precisely what I do mean," returned Dr. Giles, "and it will not seem so strange to you when I explain the precautions I intend to take against the internal heat."