When the vessel was nearly half-way to "X," the bar was reversed in order to change the sign of their acceleration, and the hollow sphere spun through an angle of one hundred and eighty degrees around the motionless cage which housed the enormous gyroscopes. Still apparently motionless and exactly as she had been before, the _Skylark_ was now actually traveling in a direction which seemed "down" and with a velocity which was being constantly decreased by the amount of their negative acceleration.
A few days after the bar had been reversed Seaton announced that the mechanical educator was complete, and brought it into the control room.
In appearance it was not unlike a large radio set, but it was infinitely more complex. It possessed numerous tubes, kino-lamps, and photo-electric cells, as well as many coils of peculiar design--there were dozens of dials and knobs, and a multiple set of head-harnesses.
"How can a thing like that possibly work as it does?" asked Crane. "I know that it does work, but I could scarcely believe it, even after it had educated me."
"That is nothing like the one Dunark used, Dick," objected Dorothy. "How come?"
"I'll answer you first, Dot. This is an improved model--it has quite a few gadgets of my own in it. Now, Mart, as to how it works--it isn't so funny after you understand it--it's a lot like radio in that respect. It operates on a band of frequencies lying between the longest light and heat waves and the shortest radio waves. This thing here is the generator of those waves and a very heavy power amplifier. The headsets are stereoscopic transmitters, taking or receiving a three-dimensional view. Nearly all matter is transparent to those waves; for instance bones, hair, and so on. However, cerebin, a cerebroside peculiar to the thinking structure of the brain, is opaque to them. Dunark, not knowing chemistry, didn't know why the educator worked or what it worked on--he found out by experiment that it did work; just as we found out about electricity. This three-dimensional model, or view, or whatever you want to call it, is converted into electricity in the headsets, and the resulting modulated wave goes back to the educator. There it is heterodyned with another wave--this second frequency was found after thousands of trials and is, I believe, the exact frequency existing in the optic nerves themselves--and sent to the receiving headset. Modulated as it is, and producing a three-dimensional picture, after rectification in the receiver, it reproduces exactly what has been 'viewed,' if due allowance has been made for the size and configuration of the different brains involved in the transfer. You remember a sort of flash--a sensation of seeing something--when the educator worked on you? Well, you did see it, just as though it had been transmitted to the brain by the optic nerve, but everything came at once, so the impression of sight was confused. The result in the brain, however, was clear and permanent. The only drawback is that you haven't the visual memory of what you have learned, and that sometimes makes it hard to use your knowledge. You don't know whether you know anything about a certain subject or not until after you go digging around in your brain looking for it."