Rollo then remembered that such a little boy was generally not interested in any one thing very long, and that, if he should let Nathan alone, he would soon put the dipper down, and then he could have it without any difficulty. So he went on making houses in the sand, and in a few minutes Nathan put the dipper down. Then, soon after, Rollo took it up and put some dry sand into it, and he found that the sand would run very smoothly, in a fine stream, through a small hole there was in the bottom of it. He determined to make an hour-glass of it. He had seen an hour-glass at his uncle George's. It was made of glass, big at the bottom and at the top, and narrow in the middle between the two. Through the narrow part in the middle, there was a very small hole, to let the sand run down through; and there was just sand enough put in to run through in an hour. So that, if a person should set the sand to running, he would know when an hour had expired, by observing when the sand had all run through. Rollo thought that he could make an hour-glass; and he thought it would be a great convenience to him to have an hour-glass in the yard; because it often happened, when he came out to play, that his mother would tell him that he might stay out an hour; and then he had to go in very often to look at the clock, in order to know exactly when the hour had expired. There were, however, so many little sticks and old leaves in the sand, that it kept getting continually clogged up, and at last Rollo began to get discouraged. He tried to pick out the little sticks; but he found he could not do that, and at last it occurred to him that probably Dorothy had some sand in the house that was cleaner. He accordingly went in and asked her. She told him that he must wash his own sand, and that would make it clean. "But haven't you got some that is clean already?" said he. "Yes," said Dorothy; "but you will like your hour-glass better if you make it all yourself." So Dorothy told him how to wash sand, for Rollo said that he did not know. She said he must put a little in a basin, and then pump water into it. "When the basin is nearly full of water, you must stir it round, and then pour off the water, and pump in more;--do this until the water comes off clear." So Rollo took the basin which Dorothy gave him, and went out to his sand-garden, and put in a little sand. Then he went to the pump, and pumped water into it. Then he stirred it about with his hand. The water immediately became very turbid, and a great many little sticks and leaves came floating up to the surface. Rollo was surprised to find how rapidly the water separated the light things which would float upon the top, from the heavy sand which would sink to the bottom. He kept pouring off the water, and pumping in more, until at length no more sticks and leaves came off, and the water appeared pretty clear. Then he carried the sand away, and spread it out upon a clean board in the sun to dry.