Now, the solution to that, thankfully, lay quite literally at hand, for he had not in all this time let go of the mallet and upon realizing this he brought it down loudly on one of the glockenspiels. Instantly Katharina sat quite still and clapped her hands over her mouth. “You mustn’t do that, I told you!” And why mustn’t I? “Because these are Father’s glockenspiels, we aren’t to touch them!” These are all Father’s glockenspiels? “All of them! All Father’s glockenspiels! All! All! All!” It doesn’t appear that he uses them, he said, and he struck another note. “He might! At any moment he might! Nothing good can come from touching Father’s glockenspiels, that’s what Wilhelmina says!” Yet the squeal she issued when he struck a third note seemed to contain not only terror but also a mischievous delight. Obviously, the astronomer said, there was nothing in the world Princess Katharina wanted more than to make music with her father’s corroding glockenspiels; why else would she sit among them? “Your turn,” he declared, and he held out the mallet. She looked at it intensely, the surfaces of her eyes seemed to strain toward it, but she made no effort to take it. “Take it, you’re allowed!” the astronomer cried, waggling the mallet. “In fact, your father has asked me to teach you music. Why do you think I’m here?” He waggled the mallet again. Tentatively she took it. “And he said we could touch the glockenspiels?” “That’s what he said,” he said, and in his head he heard himself murmur the words “within reason.” “Promise?” “Promise.” And Katharina brought the mallet down on a glockenspiel key.

The note rang out.

“I cannot describe the look on her face,” the astronomer told Leibniz, peering into his telescope, “except to say that I realized only at that instant that I would one day want a child of my own.” He added: “A colossal miscalculation, of course, as you’ll see, Herr Leibniz; how many people exist merely because their parents happened to observe a stranger’s child in an abnormally sublime moment? Such moments of abnormal sublimity among the children of strangers are probably responsible for the existence of millions. And yet, if I saw again that look on her face, I’m not sure I wouldn’t want another one.”

That, he told her, is a D-flat.