In the dark room a cloud of yellow dust flew from beneath the tool like a scatter of sparks from under the hooves of a galloping horse. The twin wheels turned and hummed. Binet was smiling, his chin down, his nostrils distended. He seemed lost in the kind of happiness which, as a rule, accompanies only those mediocre occupations that tickle the intelligence with easy difficulties, and satisfy it with a sense of achievement beyond which there is nothing left for dreams to feed on.