through that storeroom. That is what causes that normal buzzing."
It was verging on midnight when Kennedy suddenly cried: "Here, Walter, take this receiver. You remember how the buzzing sounded. Listen. Tell me if you, too, can detect the change."
I clapped the receiver quickly to my ear. Indeed I could tell the difference. In place of the loud buzzing there was only a mild sound. It was slower and lower.
"That means," he said excitedly, "that some one has entered that pitch-dark storeroom by the broken window. Let me take the receiver back again. Ah, the buzzing is coming back. He is leaving the room. I suppose he has found the electric light cane and the pistol where he left them. Now, Walter, since you have become accustomed to this thing take it and tell me what you hear."
Craig had already seized the other apparatus connected with the art-gallery and had the wireless receiver over his head. He was listening with rapt attention, talking while he waited.
"This is an apparatus," he was saying, "that was devised by Dr. Fournier d'Albe, lecturer on physics at Birmingham University, to aid the blind. It is known as the optophone. What I am literally doing now is to hear light. The optophone translates light into sound by means of that wonderful little element, selenium, which in darkness is a poor conductor of electricity, but in light is a good conductor. This property is used in the optophone in transmitting an electric current which is interrupted by a special clockwork interrupter. It makes light and darkness audible in the telephone. This thing over my head is like a wireless telephone receiver, capable of detecting a current of even a quarter of a microampere."
We were all waiting expectantly for Craig to speak. Evidently the intruder was now mounting the stairs to the art-gallery.
"Actually I can hear the light of the stars shining in through that wonderful plate glass skylight of yours, Mr. Spencer," he went on. "A few moments ago when the moon shone through I could hear it, like the rumble of a passing cart. I knew it was the moon both because I could see that it must be shining in and because I recognised the sound. The sun would thunder like a passing express-train if it were daytime now. I can distinguish a shadow passing between the optophone and the light. A hand moved across in front of it would give a purring sound, and a glimpse out of a window in daylight would sound like a cinematograph reeling off a film.
"Ah, there he is." Craig was listening with intense excitement now. "Our intruder has entered the art-gallery. He is flashing his electric light cane about at various objects, reconnoitring. No doubt if I were expert enough and had had time to study it, I could tell you by the sound just what he is looking at."
"Craig," I interrupted, this time very excited myself, "the buzzing from the high-frequency current is getting lower and lower."
"By George, then, there is another of them," he replied. "I'm not surprised. Keep a sharp watch. Tell me the moment the buzzing increases again."
Spencer could scarcely control his impatience. It had been a long time since he had been a mere spectator, and he did not seem to relish being held in check by anybody.
"Now that you are sure the vandal is there," he cut in, his cigar out in his excitement, "can't we make a dash over there and get him before he has a chance to do any more damage? He might be destroying thousands of dollars' worth of stuff while we are waiting here."
"And he could destroy the whole collection, building and all, including ourselves into the bargain, if he heard so much as a whisper from us," added Kennedy firmly.
"That second person has left the storeroom, Craig," I put in. "The buzzing has returned again full force."
Kennedy tore the wireless receiver from his ear. "Here, Walter, never mind about that electric detective any more, then. Take the optophone. Describe minutely to me just exactly what you hear."
He had taken from his pocket a small metal ball. I seized the receiver from him and fitted it to my ear. It took me several instants to accustom my ears to the new sounds, but they were plain enough, and I shouted my impressions of their variations. Kennedy was busy at the window over the heavy package, from which he had torn the wrapping. His back was toward us, and we could not see what he was doing.
A terrific din sounded in my ears, almost splitting my ear-drums. It was as though I had been suddenly hurled into a magnified cave of the winds and a cataract mightier than Niagara was thundering at me. It was so painful that I cried out in surprise and involuntarily dropped the receiver to the floor.
"It was the switching on of the full glare of the electric lights in the art-gallery," Craig shouted. "The other person must have got up to the room quicker than I expected. Here goes."
A loud explosion took place, apparently on the very window-sill of our room. Almost at the same instant there was a crash of glass from the museum.
We sprang to the window, I expecting to see Kennedy injured, Spencer expecting to see his costly museum a mass of smoking ruins. Instead we saw, nothing of the sort. On the window-ledge was a peculiar little instrument that looked like a miniature field-gun with an elaborate system of springs and levers to break the recoil.
Craig had turned from it so suddenly that he actually ran full tilt into us. "Come on," he cried breathlessly, bolting from the room, and seizing Dr. Lith by the arm as he did so. "Dr. Lith, the keys to the museum, quick! We must get there before the fumes clear away."
He was taking the stairs two at a time, dragging the dignified curator with him.
In fewer seconds than I can tell it we were in the museum and mounting the broad staircase to the art-gallery. An overpowering gas seemed to permeate everything.
"Stand back a moment," cautioned Kennedy as we neared the door. "I have just shot in here one of those asphyxiating bombs which the Paris police invented to war against the Apaches and the motor-car bandits. Open all the windows back here and let the air clear. Walter, breathe as little of it as you can—but—come here—do you see?—over there, near the other door—a figure lying on the floor? Make a dash in after me and carry it out. There is just one thing more. If I am not back in a minute come in and try to get me."
He had already preceded me into the stifling fumes. With a last long breath of fresh air I plunged in after him, scarcely knowing what would happen to me. I saw the figure on the floor, seized it, and backed out of the room as fast as I could.
Dizzy and giddy from the fumes I had been forced to inhale, I managed to drag the form to the nearest window. It was Lucille White.
An instant later I felt myself unceremoniously pushed aside. Spencer had forgotten all about the millions of dollars' worth of curios, all about the suspicions that had been entertained against her, and had taken the half-conscious burden from me.
"This is the second time I have found you here, Edouard," she was muttering in her half-delirium, still struggling. "The first time—that night I hid in the mummy-case, you fled when I called for help. I have followed you every moment since last night to prevent this. Edouard, don't, don't! Remember I was—I am your wife. Listen to me. Oh, it is the absinthe that has spoiled your art and made it worthless, not the critics. It is not Mr. Spencer who has enticed me away, but you who drove me away, first from Paris, and now from New York. He has been only—No! No!—" she was shrieking now, her eyes wide open as she realised it was Spencer himself she saw leaning over her. With a great effort she seemed to rouse herself. "Don't stay. Run—run. Leave me. He has a bomb that may go off at any moment. Oh—oh—it is the curse of absinthe that pursues me. Will you not go? Vite! Vite!"
She
