While he was thus at work preparing the sand for his hour-glass, Jonas happened to come by, and asked Rollo what he was doing. Rollo told him that he was making an hour-glass. Jonas looked on for a few minutes, and then he told Rollo that he thought that was a pretty good plan. "And _I_ am going to have a time-keeper, too," said he. "Are you?" said Rollo. "What?" "I am going to make a dial," said he. "A dial!" said Rollo; "what, a real dial?" Rollo had an idea that a dial was exceedingly complicated and difficult to make, or to understand; and, in fact, it is difficult to make one that shall be exact in its indications. He did not think it possible that Jonas could make one. "Yes," said Jonas, "a real dial; and I have got a noon mark already." "A noon mark!" said Rollo; "what is a noon mark?" "It is a mark to show when it is exactly twelve o'clock." "Let me go and see it," said Rollo, "while my sand is drying." Rollo followed Jonas off into the barn, and when there, Jonas pointed to a small line which he had cut with his penknife upon the barn floor. It began at the foot of one of the posts, by the side of the door, and extended back into the barn exactly straight. "Is that the noon mark?" said Rollo. He was surprised to see that a noon mark was nothing but a cut with a penknife upon a barn floor. "Yes," said Jonas; "that is a meridian." "A meridian!" said Rollo, looking upon it with an air of great curiosity and respect. "Yes," said Jonas; "a line drawn exactly north and south, is called a meridian line; and that is exactly north and south." "What do you call it a noon mark for?" said Rollo. "Because," said Jonas, "the shadow of the edge of the door post will always be exactly upon it at noon. So that I can always tell now when it is noon, by the shadow of the post upon my noon mark, if the sun shines." All this was very new and very curious to Rollo. He had never seen or heard of a noon mark before; and it seemed to him a very simple and beautiful way of knowing when it was noon. He asked Jonas how he found out about it, and Jonas told him that he had been reading about it in a book on astronomy. "Your father let me have the book," said he; "and see my chalk marks for the sun's shadow." Rollo looked, and found that Jonas had put down quite a number of chalk marks along in a line, where they had first began to mark the place where the shadow of the door reached into. Rollo and Lucy had forgotten all about their plan of making such a series of observations; but Jonas had gone on regularly, making a mark every Monday, at noon, precisely. As the sun, at that season of the year, was going round farther and farther to the south every week, it shone in farther and farther upon the floor, so that each chalk mark was farther in than the one made the week before.