CHAPTER XXII

IN WHICH A MATTER OF MUCH INGENUITY IS CONSIDERED

“Hello!” said Bat, his eyes almost bulging at the sight. “What the dickens is that?”

For answer the crime specialist unwound the string, drew another from the many in Scanlon’s hands, and wrapped it around the blade in turn. Once more he held up the weapon and now they read:

T O N I G H T

“I get it,” said the big man, “not all, but some. Those packages sent Miss Hohenlo had nothing at all that was worth looking at _inside_; it was _outside_ that their interest lay. In the string.”

“I think,” said the girl, wonderingly, “I’ve heard of some such a thing as this before. But it never occurred to me to apply it in this case.”

“Alva has a wooden sword the exact shape and dimensions of this,” said Ashton-Kirk, tapping the weapon. “When he desired to send a message to his confederate in Schwartzberg he’d wrap a string about the stick and carefully ink his communication, letter after letter, down its length. After this he’d unwind the cord, tie it about a parcel of blank paper and dispatch it. There was nothing about it that would excite suspicion; it held its secret until wrapped around the blade of the sword; then bit by bit the inked portion fell into place, forming the letters, and the writing was read.”

“All these strings are messages then,” said Scanlon. He frowned perplexedly, and asked: “But why write this way? Why not a letter, and a cipher inside?”

“The letter might, in some way, be opened.”

“But it couldn’t be read.”

“Perhaps not; nevertheless a cipher writing would attract notice, and in the face of such happenings as Schwartzberg has been experiencing, suspicion would be sure to follow.”

“That’s right,” said Bat. Then with a nod at the strings: “Going to read them all?”

“No,” said Ashton-Kirk. “It is hardly worth while.” He threw the heavy sword upon a table and crossed to the harp once more. “They must be very brief, and little could be got from them at best. They, for the most part, merely appointed a time for the real communications.”

“The real ones!”

“Yes; and those were received and answered upon the strings of the harp.”

Scanlon gazed at the girl, and then his eyes went wonderingly back to the other. Miss Knowles took an eager forward step.

“How?” she said.

“Upon my first visit,” said Ashton-Kirk, “I knew that you were calling my attention urgently to this instrument. And, in consequence, I took especial interest in it. I noted some peculiarities, but I did not form any conclusions until after I’d had Scanlon’s report of what he’d witnessed, and had another and specialized examination of its parts a while ago.

“The harp,” he went on, glancing at his two hearers, “is not, as a rule, a powerfully made thing. This is especially so in the case of those of this small size. The wood and the metal that go into its construction are light.” His keen glance now fixed itself upon Miss Knowles, and he asked: “Do you know whether this instrument has been sent away at any time recently for repairs?”

“It has. Shortly after we came here,” she answered. “Something was broken, I understood.”

Ashton-Kirk nodded.

“The gilding is much newer in some places than it is in others,” said he. “It’s the sign of the repairer of anything that he never does all over a job with his finishing tool, merely touching up the parts he’s worked upon.

“More than likely,” he went on, his eyes now upon the harp, “the sending of the instrument away was for a reason altogether different from the one given out. For in those parts where the tinker’s hand is plainest, I find that some very important and unusual departures have been made.”

“The upper strings are odd,” said the girl, eagerly. “I often noticed them. They are of metal.”

“And very heavy--of steel I should say; and they are strung to an astonishing tension--infinitely higher than the customary strings of the harp. The ‘pull’ of a number of steel strings of this thickness, and keyed to this pitch, would be too much for a frame of the ordinary sort. It would be pulled asunder. Consequently this one has been powerfully re-inforced; the keys are of a special type, and the sockets in which they turn appear marvellously strong.”

“But why all this?” asked Scanlon, his frowning gaze upon the harp.

“It was found necessary to establish a means of communication between the inside of Schwartzberg and the outside. Letters or written messages would not do; signal lights might be seen; secret meetings were almost impossible, for one could not often steal successfully in and out of a place watched as this one is.”

“No,” agreed Scanlon, “it couldn’t be depended on. And neither could the vaults be used as a meeting place. For the door to them is the most watched thing in the house.”

“A way must be had,” said Ashton-Kirk, “and one that must be silent and secret. This man, Alva, as Fuller’s report tells, is an able physicist, and so the method hit upon of bridging this difficulty must be his.” He looked at them as though asking their particular attention. “The eye,” said he, “is capable of vision only up to a certain point. It will follow an object going up into the air; then the object will disappear; it is ‘out of sight.’ However, though the object can’t be seen, it is still there, still going upward.

“You’ve heard the yell of the siren, a thing used upon the seagoing ships?” he proceeded. “You’ve heard its shriek mount and mount, getting higher and higher, and finally you ceased to hear it? But it had not stopped. It was still going on, only it had reached a pitch so high that it was out of ear-shot. It was only when it began to fall and had reached the point where you had lost it, that you began to hear it once more.”

Mr. Scanlon drew down one corner of his mouth and blinked a great number of times.

“What do you know about that!” said he.

“Perhaps the world’s greatest authority upon sound,” Ashton-Kirk went on as he took some notes from his pocket-book, “is the German, Helmholtz. In his book ‘On the Sensations of Tone’ he says:

“‘The simple partial tones contained in a composite mass of musical tones produce peculiar mechanical effects in nature, altogether independent of the human ear and its sensations, and altogether independent of merely theoretical considerations. These effects consequently give a peculiar objective significance to this peculiar method of analyzing vibrational forms.’

“Then,” continued Ashton-Kirk, “this master of sound goes on to speak of the phenomenon of sympathetic resonance. He says on this point: ‘When, for example, the strings of two violins are in exact unison, and one string is bowed, the other will begin to vibrate.’ And in another place: ‘Gently touch one of the keys of a pianoforte without striking the string, so as to raise the damper only, and then sing a note of the corresponding pitch, forcibly directing the voice against the strings of the instrument. On ceasing to sing the note will be echoed back from the piano. It is easy to discover that this echo is caused by the string which is in unison with the note, for directly the hand is removed from the key, and the damper is allowed to fall, the echo ceases.’

“We see, in the case of the siren, and in other things, that some tones are so high that they are not heard. Also we see, by Helmholtz, that when a string keyed to a certain tone is struck, another string, keyed to the same tone, will at once take up the sound, or vibration----”

Here Miss Knowles interrupted him, eagerly.

“I think I see what you mean,” she said. “These unusual strings upon the harp, this great strengthening of the frame, means that it is keyed to this inaudible pitch. That some one outside has an instrument of some sort keyed in unison; and when the harp string is touched, the other vibrated in sympathy.”

“And that these vibrations, made in long or short waves, or in groups, much, perhaps, as the telegraph code is made, formed a ready means of communication.”

Mr. Scanlon seemed appalled.

“Well,” said he, after a short pause, “I think I’ve absorbed the most of it. But I’m not sure. However, there is one thing I _am_ sure of, and that is that I’ve got a cabinet sized photograph of the party who’s got the other instrument. That’s what Alva had that night on the hilltop when I saw him sitting in the moonlight. He was exchanging silent talk with Schwartzberg.” Then an idea seemed to strike him, and he frowned again. “There is one thing that I don’t quite get. And that is: If these vibrations, or tones, or sounds, whatever you call them, were too high to be heard, how did the receivers of them make them out?”

Ashton-Kirk shook his head.

“As to that,” said he, “I am not prepared to say just now. A further search into the thing might bring it out, but I’m not sure. But this I will say: The sense of touch is marvellously sensitive in some people; one every now and then hears some wonderful story with regard to it. Fine, delicate hands may be the answer to your question.”

“Another thing,” said the girl. “Why was the wind required to always be from the direction of the person sending the vibrations to Schwartzberg? You’ll say to carry them. But what of the answer to them? Would not the wind which carried the vibrations from one quarter hold back those sent from the one opposite?”

“Only in part, unless the wind was very strong. And I think if you can remember the nights upon which this means of communication was used, they were fairly calm. The fact that the wind at the time of the signals was always from the direction of the person outside might be explained by that person’s superior knowledge of the medium in use. Having a more perfect understanding of it, he was the more able to read its fainter manifestations.”

Here a small clock hurriedly struck the hour of nine. And Ashton-Kirk looked at Scanlon.

“And now,” he added, “I think it’s time to drop speculation for a space. There is some work ahead of us which is going to be sharp and of the sort that leaves not even a trace of doubt in the mind.”