"Every mine has two shafts. They are a long way from each other. Only one of them is used to send the cages up and down. There is always a great fire burning at the bottom of this. The fire makes the air all round very hot, and, as all hot air is light, it rises and rushes up the shaft. As this air goes up, some more air must come from somewhere to take its place. Where do you think this other air comes from, Norah?""Does it rush down the second shaft, and along the coaly roads and streets?" asked Norah.
"That"s just it," said Fred. "What a thoughtful little girl you are!""There is always plenty of fresh air, you see, rushing through the mine. The bad gas is driven out, before it can do any harm.""Do let me tell Norah about that grand lamp, which they use in the mine." said Willie.
