"So this device does the repetition for you.
Electromechanically."

"But how?"

James smiled wistfully. "I can give you only a thumbnail sketch," he
said, "until I have had time to study the subjects that lead up to the
final theory."

"Goodness," exclaimed Mrs. Bagley, "all I want is a brief idea. I
wouldn't understand the principles at all."

"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
brain were filtered down and the extremely minute waves that ride on top
of them were amplified, the pattern of these superfine waves went through
convolutions peculiar to certain thoughts. Continued research refined
their discovery.

"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?"

"You want to memorize a list of ingredients," said James. "So you will
put this helmet on your head with the cookbook in your hands. You will
turn on the machine when yo