"Oh, a whole lot," said Mr. Blake. "If the ice is too 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."