How was hypnopaedia discovered?

From the text:

"The principle of sleep-teaching, or hypnopædia, had been discovered." The D.H.C. made an impressive pause.

The principle had been discovered; but many, many years were to elapse before that principle was usefully applied.

"The case of Little Reuben occurred only twenty-three years after Our Ford’s first T-Model was put on the market." (Here the Director made a sign of the T on his stomach and all the students reverently followed suit.) "And yet ."

Furiously the students scribbled. "Hypnopædia, *rst used of*cially in A.F. 214.

Why not before? Two reasons. (a) ."

"These early experimenters," the D.H.C. was saying, "were on the wrong track. They thought that hypnopædia could be made an instrument of intellectual education ."