During the course of his inventive life Roland Clewe had become accustomed to disappointments; he was very much afraid, indeed, that he was beginning to expect them. If that really happened, there would be an end to his career.

But when he spoke in this way to Margaret, she almost scolded him.

“How utterly absurd it is,” she said, “for a man who has just discovered the north pole to sit down in an arm-chair and talk in that way!”

“I didn't discover it,” he said; “it was Sammy and Gibbs who found the pole. As for me—I don't suppose I shall ever see it.”

“I am not so sure of that,” she said. “We may yet invent a telescope which shall curve its reflected rays over the rotundity of the earth and above the highest icebergs, so that you and I may sit here and look at the waters of the pole gently splashing around the great buoy.”

“And charge a dollar apiece to all other people who would like to look at the pole, and so we might make much money,” said he. “But I must really go and do something; I shall go crazy if I sit here idle.”

Margaret knew that the loss of the shell was the greatest blow that Roland had ever yet received. His ambitions as a scientific inventor were varied, but she was well aware that for some years he had considered it of great importance to do something which would bring him in money enough to go on with his investigations and labors without depending entirely upon her for the necessary capital. If he could have tunnelled a mountain with this shell, or if he had but partially succeeded in so doing, money would have come to him. He would have made his first pecuniary success of any importance.

“What are you going to do, Roland?” said she, as he rose to leave the room.

“I am going to find the depth of the hole that shell has made. It ought to be filled up, and I must calculate how many loads of earth and stones it will take to do it.”

That afternoon he came to Mrs. Raleigh's house.

“Margaret,” he exclaimed, “I have lowered a lead into that hole with all the line attached which we have got on the place, and we can touch no bottom. I have telegraphed for a lot of sounding-wire, and I must wait until it shall arrive before I do anything more.”

“You must be very, very careful, Roland, when you are doing that work,” said Margaret. “Suppose you should fall in!”

“I have provided against that,” said he. “I have laid a floor over the hole with only a small opening in it, so there is no danger. And another curious thing I must tell you-our line is not wet: we have struck no water!”

When Margaret visited the Works the next day she found Roland Clewe and a number of workmen surrounding the flooring which had been laid over the hole. They were sounding with a windlass which carried an immense reel of wire. The wire was extremely thin, but the weight of that portion of it which had already been unwound was so great that four men were at the handles of the windlass.

Roland came to meet Margaret as she entered.

“The lead has gone down six miles,” he said, in a low voice, “and we have not touched the bottom yet.”

“Impossible!” she cried. “Roland, it cannot be! The wire must be coiling itself up somewhere. It is incredible! The lead cannot have gone down so far!”

“Leads have gone down as far as that before this,” said he. “Soundings of more than six miles have been obtained at sea.”

She went with him and stood near the windlass. For an hour she remained by his side, and still the reel turned steadily and the wire descended into the hole.

“Shall you surely know when it gets to the bottom?” said she.

“Yes,” he answered. “When the electric button under the lead shall touch anything solid, or even anything fluid, this bell up here will ring.”

She stayed until she could stay no longer. She knew it would be of no use to urge Roland to leave the windlass. Very early the next morning a note was brought to her before she was up, and on it was written:

“We have touched bottom at a depth of fourteen and an eighth miles.”

When Roland came to Mrs. Raleigh's house, about nine o'clock that morning, his face was pale and his whole form trembled.

“Margaret,” he cried, “what are we going to do about it? It is wonderful; I cannot appreciate it. I have had all the men up in the office this morning and pledged them to secrecy. Of course they won't keep their promises, but it was all that I could do. I can think of no particular damage which would come to me if this thing were known, but I cannot bear that the public should get hold of it until I know something myself. Margaret, I don't know anything.”

“Have you had your breakfast?” she asked.

“No,” he said; “I haven't thought of it.”

“Did you eat anything last night?”

“I don't remember,” he answered.

“Now I want you to come into the dining-room,” said she. “I had a light breakfast some time ago, and I am going to eat another with you. I want you to tell me something. There was a man here the other day with a patent machine for making button-holes—you know the old-fashioned button-holes are coming in again—and if this is a good invention it ought to sell, for nearly everybody has forgotten how to make button-holes in the old way.”

“Oh, nonsense!” said Roland. “How can you talk of such things? I can't take my mind—”

“I know you can't,” she interrupted. “You are all the time thinking of that everlasting old hole in the ground. Well, I am tired of it; do let us talk of something else.”

Margaret Raleigh was much more than tired of that phenomenal hole in the earth which had been made by the automatic shell; she was frightened by it. It was something terrible to her; she had scarcely slept that night, and she needed breakfast and change of thought as much as Roland.

But it was not long before she found that it was impossible to turn his thoughts from that all-absorbing subject. All she could do was to endeavor to guide them into quiet channels.

“What are you going to do this morning?” she asked, towards the close of the breakfast.

“I am going to try to take the temperature of that shaft at various points,” said he.

“That will be an excellent thing,” she answered; “you may make valuable discoveries; but I should think the heat at that great depth would be enough to melt your thermometers.”

“It did not melt my lead or my sounding-wire,” said he. And as he said these words her heart fell.

The temperature of this great perforation was taken at many points, and when Roland brought to Margaret the statement of the height of the mercury at the very bottom she was astounded and shocked to find that it was only eighty-three degrees.

“This is terrible!” she ejaculated.

“What do you mean?” he asked in surprise. “That is not hot. Why, it is only summer weather.”

But she did not think it terrible because it was so hot; the fact that it was so cool had shocked her. In such temperature one could live! A great source of trust and hope had been taken from her.

“Roland,” she said, sinking into a chair, “I don't understand this at all. I always thought that it became hotter and hotter as one went down into the earth; and I once read that at twenty miles below the surface, if the heat increased in proportion as it increased in a mine, the temperature must be over a thousand degrees Fahrenheit. Your instrument could not have registered properly; perhaps it never went all the way down; and perhaps it is all a mistake. It may be that the lead did not go down so far as you think.”

He smiled; he was becoming calmer now, for he was doing something: he was obtaining results.

“Those ideas about increasing heat at increasing depths are old-fashioned, Margaret,” he said. “Recent science has given us better theories. It is known that there is great heat in the interior of the earth, and it is also known that the transmission of this heat towards the surface depends upon the conductivity of the rocks in particular locations. In some places the heat comes very near the surface, and in others it is very, very far down. More than that, the temperature may rise as we go down into the earth and afterwards fall again. There may be a stratum of close-grained rock, possibly containing metal, coming up from the interior in an oblique direction and bringing the heat towards the surface; then below that there may be vast regions of other rocks which do not readily conduct heat, and which do not originate in heated portions of the earth's interior. When we reach these, we must find the temperature lower, as a matter of course. Now I have really done this. A little over five miles down my thermometer registered ninety-one, and after that it began to fall a little. But the rocks under us are poor conductors of heat; and, moreover, it is highly probable that they have no near communication with the source of internal heat.”

“I thought these things were more exact and regular,” said she; “I supposed if you went down a mile in one place, you would find it as hot as you would in another.”

“Oh no,” said he. “There is nothing regular or exact in nature; even our earth is not a perfect sphere. Nature is never mathematically correct. You must always allow for variations. In some parts of the earth its heated core, or whatever it is, must be very, very far down.”

At this moment a happy thought struck Margaret.

“How easy it would be, Roland, for you to examine this great hole! I can do it; anybody can do it. It's perfectly amazing when you think of it. All you have to do is to take your Artesian, ray machine into that building and set it over the hole; then you can light the whole interior, all the way down to the bottom, and with a telescope you can see everything that is in it.”

“Yes,” said he; “but I think I can do it better than that. It would be very difficult to transfer the photic borer to the other building, and I can light up the interior perfectly well by means of electric lights. I can even lower a camera down to the very bottom and take photographs of the interior.”

“Why, that would be perfectly glorious!” cried Margaret, springing to her feet, an immense relief coming to her mind with the thought that to examine this actual shaft it would not be necessary for anybody to go down into it.

“I should go to work at that immediately,” said he, “but I must have a different sort of windlass—one that shall be moved by an engine. I will rig up the big telescope too, so that we can look down when we have lighted up the bottom.”

It required days to do all that Roland Clewe had planned. A great deal of the necessary work was done in his own establishment, and much machinery besides was sent from New York. When all was ready many experiments were made with the electric lights and camera, and photographs of inexpressible value and interest were taken at various points on the sides of this wonderful perpendicular tunnel.

At last Clewe was prepared to photograph the lower portion of the shaft. With a peculiar camera and a powerful light five photographs were taken of the very bottom of the great shaft, four in horizontal directions and one immediately below the camera. When these photographs were printed by the improved methods then in vogue, Clewe seized the pictures and examined them with eager haste. For some moments he stood silent, his eyes fixed upon the photographs as if there was nothing else in this world; but all he saw on each was an irregular patch of light. He thrust the prints aside, and in a loud, sharp voice he gave orders to bring the great telescope and set it up above the hole. The light was still at the bottom, and the instant the telescope was in position Clewe mounted the stepladder and directed the instrument downward. In a few moments he gave an exclamation, and then he came down from the ladder so rapidly that he barely missed falling. He went into his office and sent for Margaret. When she came he showed her the photographs.

“See!” he said. “What I have found is nothing; even a camera shows nothing, and when I look down through the glass I see nothing. It is just what the Artesian ray showed me; it is nothing at all!”

“I should think,” said she, speaking very slowly, “that if your sounding-lead had gone down into nothing, it would have continued to go down indefinitely. What was there to stop it if there is nothing there?”

“Margaret,” said he, “I don't know anything about it. That is the crushing truth. I can find out nothing at all. When I look down through the earth by means of the Artesian ray I reach a certain depth and then I see a void; when I look down through a perfectly open passage to the same depth, I still see a void.”

“But, Roland,” said Margaret, holding in her hand the view taken of the bottom of the shaft, “what is this in the middle of the proof? It is darker than the rest, but it seems to be all covered up with mistiness. Have you a magnifying-glass?”

Roland found a glass, and seized the photograph. He had forgotten his usual courtesy.

“Margaret,” he cried, “that dark thing is my automatic shell! It is lying on its side. I can see the greater part of it. It is not in the hole it made itself; it is in a cavity. It has turned over, and lies horizontally; it has bored down into a cave, Margaret—into a cave—a cave with a solid bottom—a cave made of light!”

“Nonsense!” said Margaret. “Caves cannot be made of light; the light that you see comes from your electric lamp.”

“Not at all!” he cried. “If there was anything there, the light of my lamp would show it. During the whole depth of the shaft the light showed everything and the camera showed everything; you can see the very texture of the rocks; but when the camera goes to the bottom, when it enters this space into which the shaft plainly leads, it shows nothing at all, except what I may be said to have put there. I see only my great shell surrounded by light, resting on light!”

“Roland,” said Margaret, “you are crazy! Perhaps it is water which fills that cave, or whatever it is.”

“Not at all,” said Roland. “It presents no appearance of water, and when the camera came up it was not wet. No; it is a cave of light.”

He sat for some minutes silently gazing out of the window. Margaret drew her chair closer to him. She took one of his hands in both of hers.

“Look at me, Roland!” she said. “What are you thinking about?”

He turned his face upon her, but said nothing. She looked straight into his eyes, and she needed no Artesian ray to enable her to see through them into his innermost brain. She saw what was filling that brain; it was one great, overpowering desire to go down to the bottom of that hole, to find out what it was that he had discovered.

“Margaret, you hurt me!” he exclaimed, suddenly. In the intensity of the emotion excited by what she had discovered, her finger-nails had nearly penetrated through his skin. She had felt as if she would hold him and hold him forever, but she released his hand.

“We haven't talked about that button-hole machine,” she said. “I want your opinion of it.” To her surprise, Roland began immediately to discuss the new invention of which she had spoken, and asked her to describe it. He was not at all anxious now to tell Margaret what he was thinking of in connection with the track of the shell.