Her reality or unreality had to be demonstrated out there, he said: “On the outside of my head.”

How, Heinrich thought, as he told the astronomer, can we tell an organism from a mechanism, objectively, outside our head, when that mechanism might be very fine, very, very delicate, as precise as you like, and engineered by a craftsman of genius?

For six days and six nights Heinrich brooded upon the conundrum in vain. At dawn on the seventh day, a Sunday, November fourteenth, “what should have been a day of rest,” the solution came to him, as blindingly obvious as such solutions tend to be: “You put her in the pump! You put her in the pump.” He understood now why he had been building pump after pump, and such big pumps to boot, “the man of science like the artist will sometimes find that his materials lead him to where his thoughts ought to go, though perhaps they fear to go there,” he had been building bigger and bigger air pumps in order to be able to put a person in one of them—or better to say, so as not to beg the question, something the size of a person, and the shape of one.

Life cannot subsist in the void, the Prince remarked, but a mechanism can. In the absence of the atmosphere a soul will grind to a halt but cogs will continue to turn.