This ebbing and flowing, which is caused by the coming in and going out of the tides, was a great puzzle to me long ago. I used often to hear the fishermen say at what hour it would be "full tide"; but I saw no mark which could help them to fix the time, and wondered, when I found their words came true, how they could know so surely. When I was older I learnt, what is very interesting, that the gradual rising of the ocean, which is called the "flow," and the gradual going back again of the water, which is called the "ebb," do not happen at any chance time, for nothing is by chance in God's creation, but at regular intervals, and in obedience to one of those wonderful rules made by God, which people call the "laws of nature"--rules which never change as the rules which men make so often do. And so we notice that for about six hours from the time when the tide begins to rise, the sea gains upon the land, either stealing on, step by step, over the pebbly beach, and creeping tip the mouths of the rivers, or, when the winds are abroad, rushing over the sand, and dashing against the rocks, as if it would sweep all before it. No power upon earth can stop that steady onward march of wave upon wave, until the unseen boundary is reached. Then we say, "It is full tide." The mighty ocean seems to pause for a few minutes, then some old fisherman, who has known that shore all his life, says, "The tide has turned"; and for six hours the gradual fall goes on. At last the lowest point of the "ebb" is reached--a few minutes' rest, and then the "flow" begins again. To those who have seen it all their lives there is nothing strange about this, but when some brave Roman soldiers, who were accustomed to conquer wherever they came, saw for the first time this ebb and flow of the tide, they were more frightened than they would have been if they had seen an army of savage men with spears and clubs rushing upon them with their fierce war-cry. They were in the presence of a power which they could not understand, and in terror they besought their general to lead them against foes whom they could face, or to take them back to their own land! By-and-by you will be interested in learning more about the tides, but I will only tell you now that they are caused by the sun and moon. Two pair of waves travel round the earth every day, the greater pair obedient to the moon, which, because she is so much nearer to us, has a greater power of drawing the water to herself than the sun has; the lesser pair obedient, in like manner, to the attraction of the sun. This is all that I can tell you now about a very difficult subject, and it is more than I told Chrissie or Ernest when we were talking about the sea; but then you know we had not much time for matters hard to be explained. One thing which I think we did talk about was the depth of the sea, and I know there were some differences of opinion about this as well as about its colour.