"Let's put it on the broom," said Susie, "and hold it up to the
ceiling."

"It's warmer up there," said Frank, looking at the little gray cylinder
when they brought it down. "It is six degrees higher than it was on the
floor."

"Why?" asked Uncle Robert.

"The heat must go up there," said Donald.

"It goes into the next room when the door is open," said Frank.

"Does it go outdoors?" asked Uncle Robert.

"Let's open the window and see," said Susie.

Frank opened the window, but, instead of feeling the warm air going out,
he felt the cool air coming in.

"Uncle," asked Donald, "isn't the room full of air already?"

"Yes," answered Uncle Robert.

"Then I don't see how any more can come in at the window."

"Are you sure none goes out?"

"I could feel it coming in," said Frank.