"Why is mercury used, uncle?" asked Frank.

"Because it takes a very great heat to make it boil." said Uncle Robert.
"Then you have seen how quickly it shows a change of temperature. When
it is warm we call it a high temperature, and when it is cold it is
called a low temperature."

"That is because the mercury goes up when it is hot, and down when it is
cold, isn't it?" said Donald. "I wonder how it would feel if it was
forty degrees below zero. See, it is away down to there!"

"Do you remember that day last winter when Peter froze his ears driving
to town?" asked Frank. "Well, it was twenty below that day at the post
office. I saw it. But father is calling me; I must go."




CHAPTER IV.

WITH THE ANIMALS.


"Don't forget to set that hen, Donald," called Mr. Leonard, as he and
Frank went away together. "I think there are enough of those Plymouth
Rock eggs for one more setting."

"You ought to see our little chickens, Uncle Robert," said Susie. "They
are just too cunning for anything."