"Fred," said Norah, "I"ve been thinking about those dreadful mines. You say there is always some of that bad gas coming out of the coal.
"I should think that, after a time, the mine would get full of it. How do the men manage to breathe down there? I wonder it does not choke them.""Teacher has made that all clear to us now," said Fred.
"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.
"All right," said Fred, "go on." "The lamp is only a simple oillamp," said Will. "But the clever part of it is that the flame is shut in all round with wire gauze. Every man lights his lamp and locks it up before he goes down. It must not be opened. The flame burns inside, but it cannot get out to the bad gas in the mine. This makes it quite safe for the men. The lamp is called the Safety Lamp.""How clever the man must have been who thought of it!" said Norah. "Yes, he was," said Fred. "Hisname was Davy, and the lamp is still called the Davy Lamp."SUMMARY
The great mass of coal down in the mine is always giving out gas. This gas will explode if a ?ame comes near it. The men use the Davy lamp, and they are quite safe, for the ?ame is shut in all round with wire gauze.
Lesson 39
