Calliope sets a copper arrow on its pin and blows gently, and it swings round, glinting in the lamp. She smiles at you over the top. "It turns for anything: a breath, a draught, a sigh. But there is one direction I never point it, and I will tell you why." The workshop smells of warm copper and the wind is up. Stand by the door, tell me which way you feel it blowing and I will tell you whether you are right.