But the machine which you see here was one recently invented for registering the temperature of sea water so as to detect the approach of an iceberg. I saw no reason why it should not be used to measure heat as well as cold.
"You see, down there I placed the couples of the thermopile beneath the electric furnace on the table. Here I have the mechanism operated by the feeble current from the thermopile, opening and closing switches, and actuating bells and lights. Then, too, I have the recording instrument. The thing is fundamentally very simple and is based on well-known phenomena. It is not uncertain and can be tested at any time, just as I did then, when I showed a slight fall in temperature. Of course it is not the slight changes I am after, not the gradual but the sudden changes in temperature."
"I see," said Carton. "If there is a drop, the current goes one way and we see the red light; a rise and it goes the other, and we see a green light."
"Exactly," agreed Kennedy. "No one is going to approach that chamber down-stairs as long as he thinks any one is watching, and we do not know where they are watching. But the moment any sudden great change is registered, such as turning on that electric furnace, we shall know it here."
It must have been an hour that we sat there discussing the merits of the case and speculating on the strange actions of Loraine Keith.
Suddenly the red light flashed out brilliantly.
"What's that?" asked Carton quickly.
"I can't tell, yet," remarked Kennedy. "Perhaps it is nothing at all. Perhaps it is a draught of cold air from opening the door. We shall have to wait see."
We bent over the little machine, straining our eyes and ears to catch the visual and audible signals which it gave.
Gradually the light faded, as the thermopile adjusted itself to the change in temperature.
Suddenly, without warning, a low-toned bell rang before us and a bright-green light flashed up.
"That can have only one meaning," cried Craig excitedly. "Some one is down there in that inferno—perhaps the bomb-maker himself."
The bell continued to ring and the light to glow, showing that whoever was there had actually started the electric furnace. What was he preparing to do? I felt that, even though we knew there was some one there, it did us little good. I, for one, had no relish for the job of bearding such a lion in his den.
We looked at Kennedy, wondering what he would do next. From the package in which he had brought the two registering machines he quietly took another package, wrapped up, about eighteen inches long and apparently very heavy. As he did so he kept his attention fixed on the telethermometer. Was he going to wait until the bomb-maker had finished what he had come to accomplish?
It was perhaps fifteen minutes after our first alarm that the signals began to weaken.
"Does that mean that he has gone—escaped?" inquired Carton anxiously.
"No. It means that his furnace is going at full power and that he has forgotten it. It is what I am waiting for. Come on."
Seizing the package as he hurried from the room, Kennedy dashed out on the street and down the outside cellar stairs, followed by us.
He paused at the thick door and listened. Apparently there was not a sound from the other side, except a whir of a motor and a roar which might have been from the furnace. Softly he tried the door. It was locked on the inside.
Was the bomb-maker there still? He must be. Suppose he heard us. Would he hesitate a moment to send us all to perdition along with himself? How were we to get past that door? Really, the deathlike stillness on the other side was more mysterious than would have been the detonation of some of the criminal's explosive.
Kennedy had evidently satisfied himself on one point. If we were to get into that chamber we must do it ourselves, and we must do it quickly.
From the package which he carried he pulled out a stubby little cylinder, perhaps eighteen inches long, very heavy, with a short stump of a lever projecting from one side. Between the stonework, of a chimney and the barred door he laid it horizontally, jamming in some pieces of wood to wedge it tighter.
Then he began to pump on the handle vigorously. The almost impregnable door seemed slowly to bulge. Still there was no sign of life from within. Had the bomb-maker left before we arrived?
"This is my scientific sledge-hammer," panted Kennedy, as he worked the little lever backward and forward more quickly—"a hydraulic ram. There is no swinging of axes or wielding of crowbars necessary in breaking down an obstruction like this, nowadays. Such things are obsolete. This little jimmy, if you want to call it that, has a power of ten tons. That ought to be enough."
It seemed as if the door were slowly being crushed in before the irresistible ten-ton punch of the hydraulic ram.
Kennedy stopped. Evidently he did not dare to crush the door in altogether. Quickly he released the ram and placed it vertically. Under the now-yawning doorjamb he inserted a powerful claw of the ram and again he began to work the handle.
A moment later the powerful door buckled, and Kennedy deftly swung it outward so that it fell with a crash on the cellar floor.
As the noise reverberated, there came a sound of a muttered curse from the cavern. Some one was there.
We pressed forward.
On the floor, in the weird glare of the little furnace, lay a man and a woman, the light playing over their ghastly, set features.
Kennedy knelt over the man, who was nearest the door.
"Call a doctor, quick," he ordered, reaching over and feeling the pulse of the woman, who had half fallen out of her chair. "They will be all right soon. They took what they thought was their usual adulterated cocaine—see, here is the box in which it was. Instead, I filled the box with the pure drug. They'll come around. Besides, Carton needs both of them in his fight."
"Don't take any more," muttered the woman, half conscious. "There's something wrong with it, Haddon."
I looked more closely at the face in the half-darkness.
It was Haddon himself.
"I knew he'd come back when the craving for the drug became intense enough," remarked Kennedy.
Carton looked at Kennedy in amazement. Haddon was the last person in the world whom he had evidently expected to discover here.
"How—what do you mean?"
"The episode of the telephone booth gave me the first hint. That is the favourite stunt of the drug fiend—a few minutes alone, and he thinks no one is the wiser about his habit. Then, too, there was the story about his speed mania. That is a frequent failing of the cocainist. The drug, too, was killing his interest in Loraine Keith—that is the last stage.
"Yet under its influence, just as with his lobbygow and lieutenant, Brodie, he found power and inspiration. With him it took the form of bombs to protect himself in his graft."
"He can't—escape this time—Loraine. We'll leave it—at his house—you know—Carton—"
We looked quickly at the work-table. On it was a gigantic bomb of clockwork over which Haddon had been working. The cocaine which was to have given him inspiration had, thanks to Kennedy, overcome him.
Beside Loraine Keith were a suit-case and a Gladstone. She had evidently been stuffing the corners full of their favourite nepenthe, for, as Kennedy reached down and turned over the closely packed woman's finery and the few articles belonging to Haddon, innumerable packets from the cabinet dropped out.
"Hulloa—what's this?" he exclaimed, as he came to a huge roll of bills and a mass of silver and gold coin. "Trying to double-cross us all the time. That was her clever game—to give him the hours he needed to gather what money he could save and make a clean getaway. Even cocaine doesn't destroy the interest of men and women in that," he concluded, turning over to Carton the wealth which Haddon had amassed as one of the meanest grafters of the city of graft.
Here