thin you will
break through, and go into the cold water. We must be very careful, I
will see if it is thick enough."

Mab waited for her father and Hal to come to where she was standing.
Roly-Poly did not wait, however. Down he rushed to the frozen pond.

"Oh, come back! Come back!" cried Mab. "You'll go through the ice,
Roly!"

But Roly-Poly paid no attention. Out on the slippery ice he ran,
and then he turned around and, looking at Daddy Blake and the two
children, he barked as loudly as he could.

Roly-Poly was a queer dog that way. Sometimes he would mind Mab, and
then, again, he would not.

"I guess the ice is thick enough to hold up Roly," said Mr. Blake. "It
doesn't need to be very strong for that, as Roly is so little."

"How thick must it be to hold us up?" Hal wanted to know.

"Well, on a small pond, ice an inch thick might hold up a little boy
or girl," explained Mr. Blake. "But not very many children at a time.
On a large pond the ice should be from six to eight inches thick to
hold up a crowd of skaters."

"Oh, does ice ever get as thick as that?" asked Hal.

"Oh, yes, and much thicker. On big lakes it gets over two feet thick
in cold weather," Mr. Blake said. "Then it will hold up a whole
regiment of soldiers, and cannon too. Ice is very strong when once it
is well frozen. But always be sure it is thick enough before going
on."

"How are you going to tell?" asked Mab.

"By cutting a little hole through the ice," her father told her. "You
can look at the edges of the hole and tell how thick the ice is. We
will try it and see."

With the big blade of his knife, Mr. Blake cut and chipped a hole in
the ice, a little way from shore. Hal and Mab stayed on the ground
watching their father, but Roly-Poly ran all about, barking as hard as
he could.

"I guess he is looking for something to bury in a hole," spoke Hal.
But Roly could not dig in the hard ice, and the ground was also frozen
too solidly for him to scratch. So all the little poodle dog could do
was to bark.

"There we are!" cried Mr. Blake, after a bit. "See, children, the ice
is more than six inches thick. It will be safe for us to skate on!"

Hal and Mab ran to look into the little hole their father had cut in
the ice. It went down for more than half a foot, or six inches, like a
well you dig in the sand at the seashore. But no water showed in the
bottom of this hole in the ice.

"The ice is good and thick," said Mr. Blake. "It wil