"We took a tuft of down, tied to a thread, and held it in the cracks and places that the air came in at, to see which way it went. We held it at the window, and it blew _in_ very strong. At the bottom of the door, it blew _in_ very strong too; but at the top, it blew _out_, into the entry. So, when the entry is full of cold air, and this room full of warm, the cold air will press in and drive out some of the warm air, into the entry. ROLLO." The other paper was also in Rollo's handwriting, and was as follows:-- "If the entry was full of water, and the parlor full of air, and the walls were water-tight, and you were to open the door between the two rooms, the water would flow into the parlor down below, and the air would flow into the entry up above. We tried it with a tuft. NATHAN." QUESTIONS. Why were Rollo and Nathan at first glad to see the rain? What did their mother say to herself on the second day, when she observed their weary and listless appearance? What did she at first direct them to do? How did she prepare the downy tuft? What experiments did they perform with it? Where did they find that the air came in which crowded the warm air up the chimney? What experiments did they perform when the door was opened? Which way did they find that the current of air was setting at the lower part of the door-way? Which way did the current set at the upper part of the door-way? What did Rollo write in his exercise? What was written in Nathan's exercise? CHAPTER IX. BURNING. After the snow had all gone off, and the ground was dry, Jonas piled up a heap of stumps, roots, and decayed logs, in a field, not far from the brook, and one sunny afternoon he and Rollo went down to set the heaps on fire. Jonas set one on fire, and then he told Rollo that he might set another on fire. After this, Jonas employed himself in gathering up sticks, bushes, roots, and other such things that lay scattered about the field, and putting them upon the fires, while Rollo amused himself in any way he pleased. After a time, Rollo found, on the margin of the field, near the edge of a wood, an old stump, taller than he was, much decayed. There was a hole in the top. Rollo climbed up so that he could put a stick in, and run it down, to see how far down the hole extended. He found that it extended down very near to the bottom. Then Rollo called out to Jonas, with a loud voice, saying,-- "Jonas, I have found a hollow stump here. It is hollow away down to the bottom. May I build a fire in it?" "Yes," said Jonas, "if you can." Rollo accordingly went to the nearest fire, and got a quantity of birch bark, which he had collected there to aid him in kindling his fires. He lighted one piece, and put it upon the end of a stick, and carried it to the stump, with the rest of the birch bark in the other hand.