"Try it," said Uncle Robert, smiling.
But no; when the edge of the glass came out of the water in the pail, down went the water with a splash.
"I see how it is," said Frank, who had watched it closely. "There wasn't any air in the glass to keep the water out, as there was when we turned it over the cork, so the water stayed in it."
"But what made it come up out of the pail?" asked Donald. "There wasn't any air under it to press it up."
"Would the air pressing on the water around the glass make it do so, uncle?" asked Frank, placing the glass in the water and raising it as Susie had done. "It seems as if it might be that."
"That is what it is," replied his uncle. "The air pressing on the water in the pail forces it into the glass, where there is nothing to keep it from rising."
"If the glass was longer would the water stay in it just the same?" asked Donald.
"Yes," was the reply. "If there was no air in the glass it would have to be very many times as long as this glass is to hold the water that would rise if it had a chance. But come, let us sit down on the steps again, and I will tell you about it."
When they were settled he continued:
"Over two hundred and fifty years ago there lived a man named Galileo, who learned a great many wonderful things by studying the stars and doing just such things as we have been doing. It was he who made the first thermometer. But there was one question that he could not answer. He found that in a hollow glass tube, closed at one end, water would rise thirty-four feet high, but no higher. He could not tell why. A pupil of his thought he would try the same thing with the heaviest liquid known——"