"What is that hole for?" asked Donald.
"So if it rains more than enough to fill this tube," explained Susie, who knew all about it, "it can run out of the hole."
"Then it will be lost," said Donald.
"No," replied Uncle Robert, "it is to be set inside of this cylinder, which is twenty-three and one-half inches long, but only six inches in diameter, and so is smaller than the top of the receiver.
"The water that runs from that hole falls into this. By measuring it in the small tube, and adding it to what the tube held before, we can know how much there is in all. One inch in the tube would be one-tenth of an inch in the receiver."
"Then twenty inches, or the tube full, would be two inches in the receiver," said Frank.
"Yes," said his uncle; "but how shall we make this stand up?"
"We might pile stones around it," suggested Donald.
"That will be a good way," said Uncle Robert.
There were some stones in a pile near the orchard fence. Frank and Donald picked them up and placed them about the rain-gauge until it stood firm.