warm kitchen. "Come, now
children," she called. "Wash your hands, and supper will soon be
ready. Then Daddy will be here, and he will shake down the furnace
fire, and make it hot, for it is going to be a very cold night."

A little later, when supper was almost ready, a step was heard in the
front hall.

"Oh, here comes Daddy now!" cried Mab, making a rush for the door.

"Let's ask him what makes the cold," exclaimed Hal, "and why we get
warm inside when we run." Hal was very curious.

"Ah, here we are!" cried Mr. Blake, with a jolly laugh, as he came in
rubbing his ears. He caught Hal up in one arm, and Mab in the other.

"Oh, how cold your cheeks are, Daddy!" cried Mab as she kissed him.

"Yes, it is going to be a frosty night, and freeze," he said. "And if
it freezes enough I will tell you a secret I have been keeping for
some time."

"Oh Daddy! Another secret!" cried Mab. "Tell us what it is, please!"

"Wait until we see if it freezes hard enough to-night," replied her
papa.

CHAPTER II

THE ICE IN THE BOTTLE

Hal and Mab were so excited at hearing their father speak about a new
secret, that they could hardly eat their supper. There were so many
questions they wanted to ask. But they managed to clear their plates,
and then, when Mr. Blake had on his slippers, and had put plenty of
coal on the furnace, Hal climbed up on one knee, and Mab on the other.

"Now, Daddy, please tell us the secret," begged the little girl.

"And tell us what makes water freeze, and how it gets cold, and what
makes us warm when we run," added Hal. "Sammie Jones is going to ask
his father what makes it lightning in a thunder storm."

"My goodness me sakes alive, and some peanut candy!" cried Daddy Blake
with a laugh. "What a lot of questions!"

"But the secret first, please," begged Mab.

"Well, let me see if it is going to be cold enough for me to tell
you," said Mr. Blake. "It must be freezing cold, or the secret will be
of no use."

Daddy Blake went to the door, outside of which hung an instrument
called a thermometer. I guess you have seen them often enough. A
thermometer is a glass tube, fastened to a piece of wood or perhaps
tin, and inside is a thin, shiny column. This column is mercury, or
quicksilver. Some thermometers have, instead of mercury, alcohol,
colored red, so it can easily be seen.

You see mercury, or alcohol, will not freeze, except in much colder
weather than you ever have where you live,