“It is true,” said Mrs. Merton, “that a canal is intended to supply the place of a river, in as far as it is useful for carrying boats; but most rivers are only deep enough in the centre for this purpose, and a great deal of ground is lost on both sides: but, when a canal is dug, it is an object to save as much ground as possible; and, therefore, the trench that is dug is equally deep in all its parts, and perfectly level at the bottom. Now, when a country is hilly, the only way in which the canal can be kept level at the bottom is, by having it in two or more parts, of different levels, each one distinct from the other; as, otherwise, all the water from the high part would run into the low part: and these little canals are joined together by means of what are called locks. Each lock is a kind of oblong well, with a pair of strong, water-tight gates at each end; the lock being just the same depth as the difference between the higher and lower parts of the canal. When a boat comes along the higher part of the canal, the gates at that end of the lock are opened, and a sufficient quantity of water flows in, to allow the boat to float in at the same level. As soon as the boat is completely within the lock, the upper gates are closed, and the gates which communicate with the lower level of the canal are opened, when the water flows out, and the boat sinks gradually down to the lower level.” “See, mamma,” cried Agnes, “there is a boat coming close to a lock; but it is in the lower part of the canal: what will they do now?” “They will open the lower gates of the lock till the water has descended to the level of that part of the canal which contains the boat, which will then float in; and, I suppose, you can guess what will then take place.” “Oh yes,” said Agnes, “the lower gates will be closed as soon as the boat is completely within the lock, and the upper ones opened.” “You are quite right,” said her mother: “and, in this way the boat will be raised to the higher level of the canal.” “I do declare, they are opening the gate now,” cried Agnes, leaning out of the window of the railway carriage as far as she possibly could. “How I do wish the train would stop a moment, and let me see the boat float in.” But it was of no use: the train whirled on; and poor Agnes, instead of watching the machinery of the lock, was obliged to sit down, and listen to a lecture from her mamma, on the impropriety of hanging out at the windows of any carriage, and of those belonging to rail-roads more particularly. Some time passed almost in silence, till at last Mr. Bevan asked Agnes if she did not admire the pretty flowers in the corn-fields they were passing. “Those poppies are very pretty, certainly,” said Agnes; “and I should admire them very much in a garden; but I do not like them in a corn field, because papa says they are a proof of bad farming.”