The room was so quiet that you noticed the ticking of the clock at once. And yet， as she now found， it was not absolutely quiet either. There was a faint.a very， very faint. humming sound. If Hoovers had been invented in those days Polly would have thought it was the sound of a Hoover being worked a long way off.several rooms away and several floors below. But it was a nicer sound than that， a more musical tone： only so faint that you could hardly hear it.
“It‘s all right； there’s no one here，” said Polly over her shoulder to Digory. She was speaking above a whisper now. And Digory came out， blinking and looking extremely dirty.as indeed Polly was too.
“This is no good，” he said. “It‘s not an empty house at all. We’d better bunk before anyone comes.”
“What do you think those are？” said Polly， pointing at the coloured rings.
“Oh come on，” said Digory. “The sooner.”
