The shape of its body, pointed both ways, helps the ?sh in its movements. The separate bones of the backbone have little hollow cups, or sockets, on both sides. The edges of the cups ?t together ; this makes the body very ?exible. The ?sh uses its tail as its propeller, to move it through the water. The other ?ns are to balance its body.
Lesson 38
Tar
"You know, Norah, that if you watch a piece of coal burn, you will see some thick, yellow smoke come from it, as well as the blaze," said Fred.
"Yes," said Will, "and it was just the same when teacher was making the gas for us in the tobacco pipe the other day. The first thing we saw was some of this same thick yellow smoke, which came puffing out from the stem.""It seems very wonderful to me," said Fred, " how one lesson leads up to another. We have learned a great many new things today by only thinking over the lesson on gas-making.
" Just picture to yourself the great retorts in thegas-works. Not only gas, but dense masses of thick smoke are given off by the coal as it burns in them. The long pipes leading from them pass into great tanks of water.
"Everything, therefore, smoke as well as gas,must pass through the water.
