Lydia smiled; but he, looking down at her, did not see the smile because of her coronet of red hair, which seemed to flame in the sunlight. The obstruction was unsatisfactory to him; he wanted to see her face. He hesitated, and then sat down on the ground beside her cautiously, as if getting into a very hot bath. “I hope you won’t mind my sitting here,” he said, timidly. “It seems rude to talk down at you from a height.” She shook her head and threw two more stones into the pool. He could think of nothing further to say, and as she did not speak, but gravely watched the circles in the water, he began to stare at them too; and they sat in silence for some minutes, steadfastly regarding the waves, she as if there were matter for infinite thought in them, and he as though the spectacle wholly confounded him. At last she said, “Have you ever realized what a vibration is?” “No,” said Cashel, after a blank look at her. “I am glad to hear you make that admission. Science has reduced everything nowadays to vibration. Light, sound, sensation--all the mysteries of nature are either vibrations or interference of vibrations. There,” she said, throwing another pair of pebbles in, and pointing to the two sets of widening rings as they overlapped one another; “the twinkling of a star, and the pulsation in a chord of music, are THAT. But I cannot picture the thing in my own mind. I wonder whether the hundreds of writers of text-books on physics, who talk so glibly of vibrations, realize them any better than I do.” “Not a bit of it. Not one of them. Not half so well,” said Cashel, cheerfully, replying to as much of her speech as he understood. “Perhaps the subject does not interest you,” she said, turning to him. “On the contrary; I like it of all things,” said he, boldly. “I can hardly say so much for my own interest in it. I am told that you are a student, Mr. Cashel Byron. What are your favorite studies?--or rather, since that is generally a hard question to answer, what are your pursuits?” Alice listened. Cashel looked doggedly at Lydia, and his color slowly deepened. “I am a professor,” he said. “A professor of what? I know I should ask of where; but that would only elicit the name of a college, which would convey no real information to me.” “I am a professor of science,” said Cashel, in a low voice, looking down at his left fist, which he was balancing in the air before him, and stealthily hitting his bent knee as if it were another person’s face. “Physical or moral science?” persisted Lydia. “Physical science,” said Cashel. “But there’s more moral science in it than people think.”