WHEN I was twelve or thirteen years old, an uncle of mine who gave me my love for books and pictures promised to take me upon a memorable expedition. I was to go with him to the top of the tower of Old Saint Lawrence in Rotterdam. And so, one fine day, a sexton with a key as large as that of Saint Peter opened a mysterious door. "Ring the bell," he said, "when you come back and want to get out," and with a great grinding of rusty old hinges he separated us from the noise of the busy street and locked us into a world of new and strange experiences.