Coal-gas is invisible. It has a powerful, unpleasant smell, and it burns with a bright ?ame. It is very explosive if mixed with air. This is the ?re-damp of the coal-mine. The Davy lamp is safe, because, although the explosive gas can enter through the gauze, and burn round the flame, the flame itself cannot pass out through the gauze.
Lesson 33
A Fish
"You know, Norah," said Fred, "that a man, a dog, or a rabbit would die if held under water, and that a fish dies as soon as it is taken out of the water. Butdon"t you think it is very strange that both die from the same cause? They both suffocate. One cannot breathe in the water, the other cannot breathe out of it. Teacher has been helping us to understand how a fish can live and breathe in the water.
"He had a fresh herring for the lesson, and as mother has bought some for supper, I asked her to let me have one to show you.
