As Kennedy walked through the corridor of the building, he paused and bent down, as though examining the wall. I looked, too. There was a crack in the concrete, in the side wall toward the Creighton laboratory.

"Do you suppose vibration caused it?" I asked, remembering his watch crystal test.

Craig shook his head. "The vibrations in a building can be shown by a watch glass full of water. You saw the surface of the liquid with its minute waves. There's vibration, all right, but that is not the cause of such cracks as these."

He stood for a moment regarding the crack attentively. On the floor on which we were was the Consolidated Bank itself. Beneath us were the Consolidated Safety Deposit vaults.

"What did cause them, then?" I asked, mystified.

"Apparently escaping currents of electricity are causing electrolysis of the Bank Building," he replied, his face wrinkled in thought.

"Electrolysis?" I repeated mechanically.

"Yes. I suppose you know how stray or vagrant currents affect steel and concrete?"

I shook my head in the negative.

"Well," he explained as we stood there, "I believe that in one government test at least it was shown that when an electric current of high voltage passes from steel to concrete, the latter is cracked and broken. Often a mechanical pressure as great as four or five thousand pounds a square inch is exerted and there is rapid destruction due to the heating effect of the current."

I expressed my surprise at what he had discovered. "The danger is easily overestimated," he hastened to add. "But in this case I think it is real, though probably it is a special and extreme condition. Still it is special and extreme conditions which we are in the habit of encountering in our cases, Walter. That is what we must be looking out for. In this instance the destruction due to electrolysis is most likely caused by the oxidation of the iron anode. The oxides which are formed are twice as great in volume as the iron was originally and the resulting pressure is what causes the concrete to break. I think we shall find that this condition will bear strict watching."

For a moment Kennedy stopped at the little office of the superintendent of the building, in the rear.

"I was just wondering whether you had noticed those cracks in the walls down the corridor," remarked Kennedy after a brief introduction.

The superintendent looked at him suspiciously. Evidently he feared we had some ulterior motive, perhaps represented some rival building and might try to scare away his tenants.

"Oh, that's nothing," he said confidently. "Just the building settling a bit—easily fixed."

"The safety vault company haven't complained?" persisted Kennedy, determined to get something out of the agent.

"No indeed," he returned confidently. "I guess they've got troubles of their own—real ones."

"How's that?" asked Craig, falling in with the man's evident desire to change the subject.

"Why, I believe their alarm system's out of order," he replied. "Some of the fine wires in it burnt out, I think. Defective wiring, I guess. Oh, they've had it patched up, changed about a little,—it's all right now, they say. But they've had a deuce of a time with the alarm ringing at all sorts of hours, and not a trace of trouble."

I looked quickly at Craig. Though the superintendent thought he had been very clever in changing the topic of conversation, he had unwittingly furnished us with another clew. I could not ask Craig before him and I forgot to do so later, but, to me at least, it seemed as if this might be due to induction from the stray currents.

"No one here seems to have suspected the Creighton motor, anyhow," commented Craig to me, as we thanked the superintendent and walked across to the elevators.

We rode up to Tresham's office, which was on the third floor, on the side of the building toward Creighton's laboratory. In fact one of the windows opened almost on the roof of the brick building next door.

We found Tresham in his office and he received us affably, I thought. "Miss Laidlaw told me she was going to consult you," he remarked as we introduced ourselves. "I'm glad she did so."

Tresham was a large, well-built fellow, apparently athletically inclined, clean shaven with dark hair that was getting very thin. He seemed quite at ease as he talked with us, yet I could tell that he was weighing us all the time, as lawyers will do.

"What do you think of Creighton's motor?" opened Kennedy. "You've seen it, I suppose?"

"Oh, yes," he replied quickly and jerkily. "Since Miss Laidlaw became interested he's been in here to have me look over his application for a patent. You know, I used to be a patent lawyer for a number of years until I decided to branch out into general practice. Legally Creighton seems to be sound enough. Of course, you know, the patent office won't grant a patent on a machine such as he claims without a rigid demonstration. He needs money, he says, for that. If his idea is sound, I don't see any reason why he shouldn't get a basic patent."

Tresham paused. I was conscious that he was furtively watching the face of Kennedy as though he hoped to learn as much from him as Craig did on his part.

"It's the mechanical end of it that I don't understand," continued Tresham, after a pause. "Creighton claims to have discovered a new force which he calls vibrodyne. I think it is just as well that Miss Laidlaw has decided to consult a scientist about it before she puts any more money into the thing. I can't say I approve of her interest in it—though, of course, I know next to nothing about it, except from the legal standpoint."

"Who is that Mrs. Barry of whom Miss Laidlaw spoke?" asked Kennedy a moment later.

"I believe she is a friend of Creighton's. Somehow she got acquainted with Miss Laidlaw and introduced her to him."

"You know her?" queried Craig casually.

"Oh, yes," came the frank reply. "She has been in to see me, too; first to interest me in the motor, and then to consult me about various legal points in connection with it."

I felt sure that Tresham was more than just a bit jealous of his pretty client. Certainly his tone was intended to convey the impression that he wished she would leave her affairs in his hands entirely.

"You don't know anything more about her—where she came from—her connections?" added Craig.

"Hardly more than you do," asserted Tresham. "I've only seen the woman a few times. In fact I should be glad to know more about her—and about Creighton, too. I hope that if you find out anything you'll let me know so that I can protect Miss Laidlaw's interests."

"I shall do so," promised Kennedy, rising.

"I'll do the same," agreed Tresham, extending his hand. "I see no reason why we shouldn't work together for—my client."

There was no mistaking the fact that Tresham would have liked to be able to say something more intimate than "client." Perhaps he might have been nearer to it if her interest in him had not been diverted by this wonderful motor. At any rate I fancied he had little love for Creighton. Yet, when I reflected afterward, it seemed like a wide gulf that must separate a comparatively impecunious lawyer from a wealthy girl like Adele Laidlaw.

Kennedy was not through with his effort to learn something by a thorough investigation of the neighborhood yet. For some time after we left Tresham's office, he stood in the doorway of the Bank Building, looking about as though he hated to leave without establishing some vantage point from which to watch what was going on in Creighton's laboratory.

"Of course I can't very well get into the safety vault under the bank," he mused. "I wish I could."

He walked past Creighton's without seeing anything happen. The next building was a similar two-story brick affair. A sign on it read, "Studios and Offices For Rent."

An idea seemed to be suggested to him by the sign. He wheeled and entered the place. Inquiry brought out a caretaker who showed us several rooms unoccupied, among them one vacant on the first floor.

Kennedy looked it over carefully, as though considering whether it was just the place he wanted, but ended, as I knew he intended, in hiring it.

"I can't move my stuff in for a couple of days," he told the caretaker. "Meanwhile, I may have the key, I suppose?"

He had paid a good deposit and the key was readily forthcoming.

The hiring of the ground floor room accomplished without exciting suspicion, Kennedy and I made a hasty trip up to his own laboratory, where he took a small box from a cabinet and hurried back to the taxicab which had brought us uptown.

Back again in the bare room which he had acquired, Craig set to work immediately installing a peculiar instrument which he took from the package.

It seemed to consist of two rods much like electric light carbons, fixed horizontally in a wooden support with a spindle-shaped bit of carbon between the two ends of the rods. Wires were connected with binding screws at the free ends of the carbon rods.

First Craig made a connection with an electric light socket from which he removed the bulb, cutting in a rheostat. Then he attached the free wires from the carbons to a sort of telephone headgear and switched on the current.

"What is it?" I asked curiously.

"A geophone," he replied simply.

"And what is a geophone?" I inquired.

"Literally an earth-phone," he explained. "It is really the simplest form of telephone, applied to the earth. You saw what it was. Any high school student of physics can make one, even with two or three dry batteries in circuit."

"But what does it do?" I asked.

"It is really designed to detect earth vibrations. All that is necessary is to set the carbon stick arrangement, which is the transmitter of this telephone, on the floor, place myself at the other end and listen. A trained ear can readily detect rumblings. Really it is doing in a different and often better way what the seismograph does. This instrument is so sensitive that it will record the slamming of a cellar door across the street. No one can go up those stairs next door without letting me know it, no matter how cautious he is about it."

Craig stood there some minutes holding the thing over his ears and listening intently.

"The vibrodyne machine isn't running," he remarked finally after repeated adjustments of the geophone. "But someone is in that little room under Creighton's workshop. I suspected that something was down there after that watch crystal test of mine. Now I know it. I wonder what the man is doing?"

There was no excuse yet, however, for breaking into the room on the other side of the wall and under Creighton's. Kennedy went out and watched. Though we waited some time nobody came out. He went back to our own room in the rear of the first floor. Though we both listened some time, neither of us could now hear a sound through the geophone except those made by passing trolleys and street vehicles.

Inquiry about the neighborhood did not develop who was the tenant or what was his business. In fact the results were just the reverse. No one seemed to know even the business conducted there. The room back of the locked door which Miss Laidlaw had passed was shrouded in mystery.

Nothing at all of any value was being recorded by the geophone when Kennedy glanced quickly at his watch. "If we are to see Miss Laidlaw and meet that Mrs. Barry, we had better be on our way," he remarked hurriedly.

Miss Laidlaw was living in a handsome apartment on Central Park, West. We entered and gave our cards to the man at the door of her suite, who bowed us into a little reception room. We entered and waited.

Suddenly we were aware that someone in the next room, a library, was talking. Whether we would or not we could not help overhearing what was said. Apparently two women were there, and they were not taking care how loud they spoke.

"Then you object to my even knowing Mr. Creighton?" asked one of the voices, pausing evidently for a reply which the other did not choose to make. "I suppose if it was Mr. Tresham you'd object, too."

There was something "catty" and taunting about the voice. It was a hard voice, the voice of a woman who had seen much, and felt fully capable of taking care of herself in more.

"You can't make up your mind which one you care for most, then? Is that it?" pursued the same voice. "Well, I'll be a sport. I'll leave you Creighton—if you can keep him."

"I want neither," broke in a voice which I recognized at once as Adele Laidlaw's.

She spoke with a suppressed emotion which plainly indicated that she did want one of them.

Just then the butler entered with our cards. We heard no more. A moment later we were ushered into the library.

Mrs. Barry was a trim, well-groomed woman whose age was deceptive. I felt that no matter what one might think of Miss Laidlaw, here was a woman whose very looks seemed to warn one to be on his guard. She was a woman of the world, confident in her own ability to take care of herself.

Adele was flushed and excited, as we entered, though she was making a desperate effort to act as though nothing had happened.

"My friend, Professor Kennedy, and Mr. Jameson," she introduced us simply, making no pretense to conceal our identity.

Mrs. Barry was, in addition to her other accomplishments, a good actress. "I've heard a great deal about you, Professor," she said, extending her hand, but not taking her eyes off Craig's face.

Kennedy met her gaze directly. What did she mean? Had she accepted Miss Laidlaw's invitation to call in order to look us over, knowing that we had come to do the same?

"Mr. Creighton tells me that you have been to see his new motor," she ventured, even before any of us could open the subject.

She seemed to enjoy making the remark for the specific purpose of rousing Miss Laidlaw. It succeeded amply, also. The implication that Creighton took her into his confidence was sufficient to cause Adele Laidlaw to shoot an angry glance at her.

Mrs. Barry had no objection to sticking a knife in and turning it around. "Of course I don't know as much about such things as Miss Laidlaw," she purred, "but Mr. Tresham tells me that there may be some trouble with the patent office about allowing the patent. From all I have heard there's a fortune in that motor for someone. Wonderful, isn't it?"

Even the mention of Tresham's name in the studied familiarity of her tone seemed to increase the scarcely latent hostility between the two women. Kennedy, so far, had said nothing, content merely to observe.

"It appears to be wonderful," was all he said, guardedly.

Mrs. Barry eyed him sharply and Miss Laidlaw appeared to be ill at ease. Evidently she wanted to believe in Creighton and his motor, yet her natural caution forbade her. The entrance of Kennedy into the case seemed to have proved a disturbing factor between the two women, to have brought matters to a head.

We chatted for a few minutes, Kennedy deftly refusing to commit himself on anything, Mrs. Barry seeking to lead him into expressing some opinion, and endeavoring to conceal her exasperation as he avoided doing so.

At last Kennedy glanced at his watch, which reminded him of a mythical appointment, sufficient to terminate the visit.

"I'm very glad to have met you," he bowed to Mrs. Barry, as she, too, rose to go, while he preserved the fiction of merely having dropped in to see Miss Laidlaw. He turned to her. "I should be delighted to have both you and Mr. Tresham drop in at my laboratory some time, Miss Laidlaw."

Miss Laidlaw caught his eye and read in it that this was his way, under the circumstances, of asking her to keep in touch with him.

"I shall do so," she promised.

We parted from Mrs. Barry at the door of her taxicab.

"A very baffling woman," I remarked a moment later. "Do you suppose she is as intimate with Creighton as she implies?"

Kennedy shook his head. "It isn't that that interests me most, just now," he replied. "What I can't figure out is Adele Laidlaw's attitude toward both Creighton and Tresham. She seems to resent Mrs. Barry's intimacy with either."

"Yes," I agreed. "Sometimes I have thought she really cared for both—at least, that she was unable to make up her mind which she cared for most. Offhand, I should have thought that she was the sort who wouldn't think a man worth caring much for."

Kennedy shook his head. "Given a woman, Walter," he said thoughtfully, "whose own and ancestral training has been a course of suppression, where she has been taught and drilled that exhibitions of emotion and passion are disgraceful, as I suspect Miss Laidlaw's parents have believed, and you have a woman whose primitive instincts have been stored and strengthened. The instincts are there, nevertheless, far back in the subconscious mind. I don't think Adele Laidlaw knows it herself, but there is something about both those men which fascinates her and she can't make up her mind which fascinates her most. Perhaps they have the same qualities."

"But Mrs. Barry," I interrupted. "Surely she must know."

"I think she does," he returned. "I think she knows more than we suspect."

I looked at him quickly, not quite making out the significance of the remark, but he said no more. For the present, at least, he left Adele Laidlaw quite as much an enigma as ever.

"I wish that you would make inquiries about regarding Mrs. Barry," he said finally as we reached the subway. "I'm going down again to the little room we hired and watch. You'll find me at the laboratory later tonight."