"If you sought to break a castle wall, Geoffrey," Fess explained, "that purpose would turn back on you, and it is yourself who would be broken."
That brought Geoffrey up short. "Mayhap I should not wish it," he said slowly.
"Only 'mayhap'?" Cordelia said aghast, watching him out of the corner of her eye.
"But there is worse to tell." Fess's voice was flat and toneless. "That tenfold thought would still be projected out of you again, and the wall would return it to your mind, multiplied by another ten…"
"An hundred times stronger!" Cordelia breathed.
"Exactly. And the hundredfold signal would push out, to be returned multiplied by ten yet again."
"A thousandfold." Geoffrey was definitely beginning to see the horror of it.
"Yes, Geoffrey; we call such a phenomenon a 'feedback loop.' And, being uncontrolled…"
"It would burn out his mind," Magnus whispered.
"It would, if you did not cease pushing out your thoughts almost instantly. Fortunately, your father knows what feedback is, and ceased the experiment as soon as he felt his own mental power turning back on him. Even so, he had a raging headache, and I kept a close watch on him for twenty-four hours, fearing brain damage."
"That was when he failed to come home!" Geoffrey exclaimed.
"No wonder thou wast so distraught," Cordelia said to Gwen.
"I was quite concerned," Gwen admitted, "though Fess sought to reassure me."
"I immediately informed her that he was well, but would rest within the spaceship for the night. He had connected me to its systems, as he does whenever he goes there, so I was able to monitor his condition closely through his sickbed. But he recovered, with no sign of brain damage."
"Did he ever dare use it again?"
"I dislike that glint in your eye, Geoffrey. Please give over any thought of using the device; it is simply too powerful."
"But is it truly safe where it is?" Gregory asked.
"The friars of St. Vidicon of Cathode have sifted such matters five hundred years," Gwen assured them.
"And five centuries of research into psionic affairs should give them a certain competence," Rod pointed out. "In fact, Brother Al assured me they were the best in the Terran Sphere, even better than the scholars on Terra."
"If they cannot handle it safely," Fess said, "no one can—and they will have the good sense to know that at once."
"Then they may destroy it?" Gregory sounded so disappointed that Fess interpreted it as a danger signal, but his programming wouldn't allow him to lie. "I cannot be certain, Gregory, for your father asked them not to tell him if they did so."
"I was kinda proud of it," Rod admitted.
"So," Fess said, "they may liquidate it—or they may yet use it as a research tool. We simply do not know."
"Yet we can know that we will never have it out from there," Geoffrey said, disgusted.
"Quite so, Geoffrey." Fess was relieved to see his most tenacious student finally let go of the notion. "Destroyed or intact, it has gone where it will be safe."
Geoffrey suddenly lurched, tripping over something among the dry leaves. "Ouch!"
They were all suddenly still, for there had been a very odd echo to his word.
In the silence, they heard music.
"'Tis louder," Gregory observed.
"And with a stronger fundament." Geoffrey's head began jerking backward and forward in time to the beat.
"Geoffrey," Fess commanded, "hold still!"
The boy looked up at him, hurt. "I did not move, Fess."
"Yet thou didst," Gregory assured him, and turned to Fess, wide-eyed. "What insidious thing is this, Fess, that doth make one's body to move without his own awareness?"
"It is rock music, Gregory," Fess answered. "Come, look where Geoffrey tripped."
They turned back a step and pushed aside the leaves. Sure enough, there it lay, the twin of the first rock they had found.
"We were right!" Cordelia cried, clenching her fists and hopping with delight. "Oh! Hath our experiment succeeded, Fess?"
"It has, Cordelia; our hypothesis is validated. Now, gather more data."
"Well enough!" Cordelia knelt and picked up the rock. It chuckled. "Oh!" she said, surprised. "Tis harder!"
"Yet still doth yield." Geoffrey poked the rock with a finger, and it fairly howled with laughter.
"Let me! Let me!" Gregory dropped down to probe the stone, and it laughed so hard it coughed—right on the beat, of course. "Leave off!" it wheezed between coughs. "Oh! I shall die of tickling!"
Cordelia dropped it and rubbed her hands on her skirt.
"Art thou alive, then?" Gregory asked.
"Aye; no fossil form am I." The rock chuckled. "Oh! I have not laughed so since last I split!"
"Last?" Magnus looked up. "Thou dost halve oft, then?"
"Have off what?… Oh!" The rock chortled. "Aye, foolish lad! Whene'er I increase far enough!"
"Didst thou divide today?"
"Divide today into what? Oh! Morn and afternoon, of course! Nay, I did not—the sun did that."
"Whose son? Oh! Thou dost speak of the orb in the sky! Yet didst thou split when it rose to its highest?"
"Aye, lad, every day I havel 'Tis fertile land here, midst the leaves! And I do take my leave when'er I may!"
"Dost thou never work, then?"
"Nay, I exist but to make music! A bonny life it is!"
"So long as there is witch-moss by for thou to roll into," Cordelia returned. "Yet wherefore art thou hardened?"
"Why, for that I've aged. All things must needs grow hard as they grow old."
"Not every thing," Rod said quickly, with a glance at Gwen.
"It is not entirely true," Fess agreed. "Still, I must admit that is the common progression."
"Yet an it hath progressed as its progenitor did…" Magnus stood, gazing thoughtfully off into the trees.
"Aye." Gregory pointed. "Yon doth continue the vector we did tread, brother!"
"Another hypothesis?" Fess was ever alert for the sounds of learning.
"Nay, further evidence for the one we've tested. An we backtrack farther on this vector, Fess, we should discover the parent of this parent rock."
Fess nodded judiciously. "That is a warranted extrapolation, boys. Yet time grows short; let us send the spy-eye." The pommel of his saddle sprang up, and a metal egg rose out of it.
"Fun!" Cordelia cried, and the children crowded around Fess's withers, where a section of his hide slid up to expose a video screen that glowed to life, showing a bird's-eye view of the immediate area. They could see Fess's head, neck, and back with their own four heads clustered around, growing smaller in the screen and swinging off to the left.
"I did not know of this," Gwen told Rod.
"Never thought to tell you," he admitted. "Remind me to dig up his specifications chart for you one of these days."
The rock increased the volume of its music, miffed at being so suddenly ignored.
"Cordelia," Gwen said, "cease tapping thy foot."
Cordelia glowered, but stopped.
On the screen, greenery streamed past faster and faster as the spy-eye shot toward the west. Then, suddenly, it slowed to a halt.
"Three hundred meters," Fess said, "the same distance we have come from the first stone. Here is the audio, children."
From the grille below the screen music blared, faster than that in the air around them, and with a heavier beat. The music from the speaker jarred with the music around them, out of phase; the children winced, and Fess turned it down. "There is another music rock nearby, of a certainty. Let the eye descend, Fess."
The leaves on the screen seemed to swim upward, past the edges of the frame and out, until the brown of fallen leaves filled the screen. The brush swelled until the children could see the outlines of each stick and branch.