"Stand over there in front of the helix," Standish said. "I don't think there's any danger. Unless I'm wrong, the thing simply places the patient in an electro magnetic field and transmits an alternating vibration to the human brain."

He played with the dials a long time, twisted a rheostat experimentally.

"Notice anything?"

"Yes, I ..." The Earth girl's voice died off. A vacant look entered her eyes. "What is your wish?" she asked suddenly.

Standish made a quick adjustment to the controls. "Sit down," he commanded.

Obediently, Thalia moved across to a chair and sat stiffly erect.

"You have studied some mathematics," Standish said then. "Tell me, what is the principal of the algebraic curve?"

Without hesitation Thalia replied, "A curve, the equation of which contains no transcendental quantities; a figure the intercepted diameters of which bear always the same proportion to their respective ordinates."

Standish uttered a low cry of triumph and threw over the reverse lever of the machine. An instant later Thalia stared at him in bewilderment.

"What happened?"

"It worked," Standish replied. "With that device and a hundred more like it I will build, I can control every last Sirian prisoner. I can make them help us build an entire fleet, using all their scientific knowledge."

Thalia's eyes glowed. "We'll be fighting them with their own people," she said.

IX

The electro-hypnosis machines finished, Standish enlisted Ga-Marr's aid and proceeded to try them on a group of Sirian prisoners.

"After all," the Earthman said, "what we're doing is for the sake of your planet and mine. These prisoners will suffer no ill effect, but by organizing their efforts, we can aid a great cause."

He turned a control knob, and a low hum sounded in the machine. The green liquid in the globe began to bubble, and a column of mist climbed upward through the connecting tube.

Improved as they were by Standish, the machines 

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