She thought. "Why, by repeating and repeating and rehearsing and rehearsing."

"Yes," said James. "So this device does the repetition for you. Electromechanically."

"But how?"

"...Well, then, my mother, as a cerebral surgeon, knew the anatomy of the human brain. My father, as an instrument maker, designed and built encephalographs. Together, they discovered that if the great waves of the human brain were filtered down and the extremely minute waves that rode on top of them were amplified, the pattern of these superfine waves went through convolutions peculiar to certain thoughts..."

"Now, the general theory is that the cells of the brain act sort of like a binary digital computer, with certain banks of cells operating to store sufficient bits of information to furnish a complete memory. In the process of memorization, individual cells become activated and linked by the constant repetition.

"Second, the brain within the skull is a prisoner, connected to the 'outside' by the five standard sensory channels of sight, sound, touch, taste, and smell. Stimulate a channel, and the result is a certain wave-shape of electrical impulse that enters the brain and—sort of like the key to a Yale lock—fits only one combination of cells. Or if no previous memory is there, it starts its own new collection of cells to linking and combining. When we repeat and repeat, we are deepening the groove, so to speak.

"Finally comes the Holden Machine. The helmet makes contact with the skull in those spots where the probes of the encephalograph are placed. When the brain is stimulated into thought, the brain waves are monitored and recorded, amplified, and then fed back to the same brain-spots. Not once, but multifold, like the vibration of a reed or violin string. The circuit that accepts signals, amplifies them, returns them to the same set of terminals, and causes them to be repeated several hundred times per millisecond without actually ringing or oscillating is the real research secret of the machine. My father's secret and now mine."

"And how do we use it?"