He was not a Mozart. No. But he was somebody, as I was to find out, quite as extraordinary. It was one morning in the early summer that I made the discovery. I was sitting in the warm shade of our westward-facing balcony, working. Guido and Robin were playing in the little enclosed garden below. Absorbed in my work, it was only, I suppose, after the silence had prolonged itself a considerable time that I became aware that the children were making remarkably little noise. There was no shouting, no running about; only a quiet talking. Knowing by experience that when children are quiet it generally means that they are absorbed in some delicious mischief, I got up from my chair and looked over the balustrade to see what they were doing. I expected to catch them dabbling in water, making a bonfire, covering themselves with tar. But what I actually saw was Guido, with a burnt stick in his hand, demonstrating on the smooth paving-stones of the path, that the square on the hypotenuse of a right-angled triangle is equal to the sum of the squares on the other two sides. Kneeling on the floor, he was drawing with the point of his blackened stick on the flagstones. And Robin, kneeling imitatively beside him, was growing, I could see, rather impatient with this very slow game. “Guido,” he said. But Guido paid no attention. Pensively frowning, he went on with his diagram. “Guido!” The younger child bent down and then craned round his neck so as to look up into Guido’s face. “Why don’t you draw a train?” “Afterwards,” said Guido. “But I just want to show you this first. It’s so beautiful,” he added cajolingly. “But I want a train,” Robin persisted. “In a moment. Do just wait a moment.” The tone was almost imploring. Robin armed himself with renewed patience. A minute later Guido had finished both his diagrams. “There!” he said triumphantly, and straightened himself up to look at them. “Now I’ll explain.”