"How are we to know we're in the next house but one?" They decided they would have to go out into the boxroom and walk across it taking steps as long as the steps from one rafter to the next. That would give them an idea of how many rafters went to a room. Then they would allow about four more for the passage between the two attics in Polly's house, and then the same number for the maid's bedroom as for the box-room. That would give them the length of the house. When they had done that distance twice they would be at the end of Digory's house; any door they came to after that would let them into an attic of the empty house.
"But I don't expect it's really empty at all," said Digory.
"What do you expect?"
"I expect someone lives there in secret, only coming in and out at night, with a dark lantern. We shall probably discover a gang of desperate criminals and get a reward. It's all rot to say a house would be empty all those years unless there was some mystery."
"Daddy thought it must be the drains," said Polly.
"Pooh! Grown-ups are always thinking of uninteresting explanations," said Digory. Now that they were talking by daylight in the attic instead of by candlelight in the Smugglers' Cave it seemed much less likely that the empty house would be haunted.
When they had measured the attic they had to get a pencil and do a sum. They both got different answers to it at first, and even when they agreed I am not sure they got it right. They were in a hurry to start on the exploration.
"We mustn't make a sound," said Polly as they climbed in again behind the cistern. Because it was such an important occasion they took a candle each (Polly had a good store of them in her cave).
It was very dark and dusty and draughty and they stepped from rafter to rafter without a word except when they whispered to one another, "We're opposite your attic now" or "this must be halfway through our house". And neither of them stumbled and the candles didn't go out, and at last they came where they could see a little door in the brick wall on their right. There was no bolt or handle on this side of it, of course, for the door had been made for getting in, not for getting out; but there was a catch (as there often is on the inside of a cupboard door) which they felt sure they would be able to turn.
"Shall I?" said Digory.
"I'm game if you are," said Polly, just as she had said before. Both felt that it was becoming very serious, but neither would draw back. Digory pushed round the catch with some difficultly. The door swung open and the sudden daylight made them blink. Then, with a great shock, they saw that they were looking, not into a deserted attic, but into a furnished room. But it seemed empty enough. It was dead silent. Polly's curiosity got the better of her. She blew out her candle and stepped out into the strange room, making no more noise than a mouse.
It was shaped, of course, like an attic, but furnished as a sitting-room. Every bit of the walls was lined with shelves and every bit of the shelves was full of books. A fire was burning in the grate (you remember that it was a very cold wet summer that year) and in front of the fire-place with its back towards them was a high-backed armchair. Between the chair and Polly, and filling most of the middle of the room, was a big table piled with all sorts of things printed books, and books of the sort you write in, and ink bottles and pens and sealing-wax and a microscope. But what she noticed first was a bright red wooden tray with a number of rings on it. They were in pairs - a yellow one and a green one together, then a little space, and then another yellow one and another green one. They were no bigger than ordinary rings, and no one could help noticing them because they were so bright. They were the most beautiful shiny little things you can imagine. If Polly had been a very little younger she would have wanted to put one in her mouth.
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 alright; 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.