"I kind of take it for granted that our great-grandchildren will regard us as a sort of precursor species. That they won't think of us as human and if we could see them, we probably wouldn't think of them as human either."
- William Gibson

How did the brain work?

A crystal such as this beryl, he said, was a drawdng together of matter into individual units of latent thought. Crystalline structures, with their angles and planes and molecular groupings, constituted the sum total of mathematics, the alpha and omega of electrical, mechanical, and chemical law.

No, the Brain wouldn’t have to be taught, he declared; and before that night was over I fully agreed with him...

NOW it came clumping across the laboratory floor with this platinum pot, placing it on the workbench, underneath and in the full illumination of an overhanging electric bulb.

Martery’s excitement reached fever heat.

“Heavens!” he gasped, between teeth that were still clenched on the stem of his long-dead pipe. “It’s going to mix up something!”

The created material opens up a rift in space. Both men are pulled into it. The brain and its robot body disappear. The author speculates:

Perhaps the Brain had wanted to get away, and had used its alien knowledge coupled with some subtle alchemy in erecting this avenue of escape. And as it withdrew it had inadvertently carried us along with it. Possibly its unhuman reason taught it of some extra space, some ulterior abyss or dimension, uncomprehended by man.

Or possibly the Brain’s consciousness had its real existence in some outer space. Perhaps the beryl crystal was but some integral part of a vaster organism projected into our three dimensioned space, a feeler or tentacle, extending along a fourth dimension, which it had chosen to withdraw.

Thus I reasoned. And on top of this came the sudden discovery that my hands and arms — in fact all parts of my body — were invisible to me. I held my hands over my eyes. They in no way impaired that strange sense of vision, for I could still see that ash-gray plane stretching infinitely away in all directions from me.