terior of the earth, and it threatens to continue increasing in the same manner for some time to come. As this heat might injure the tube, I shall be forced to remove it in some way."
"Remove the heat?" said Mr. Curtis, inquiringly.
"Of course; the only way to get rid of heat is to remove it."
"But in your first plan of pumping cold liquids through the tube, you did n't remove any heat."
"If that plan had been adopted it would most certainly have resulted in removing the heat, and that is precisely where its weak point lies. The heat would have passed into the cold liquids, and these would soon have become so hot that the pumping operations would have had to be on a gigantic scale to keep the tube at the proper temperature."
"Ah! and what is your new plan?"
"My new plan is simply to transform the internal heat into electricity, and then carry off this electricity from the tube by means of special conductors."
""What!" exclaimed Mr. Curtis, "you think you will be able to change the heat into electricity?"
"Certainly," said Dr. Giles. "Did you not know that heat, force, light, and electricity are
