"Yes," replied their father, "I presume it would make a loud explosion; that is, if the air in the room around it could by any means be all at once and suddenly removed.
"And so you must remember," he continued, "that there are two very remarkable differences between air and water. Air may be condensed by pressure, and, as it exists all around us, is greatly condensed by the pressure of the air above, and it may be compressed more. And air is expansive, while water is not. Whenever the pressure upon it is removed, it suddenly expands, or spreads out in all directions."
"O dear me!" said Nathan, with a sigh.
"What is the matter?" said his father.
"Why, I can't understand it very well."
"Can't you?" said his father. "Well, I must admit that you are rather too young to study pneumatics."
"Pneumatics?" repeated Rollo.
"Yes," said his father; "that is the name of this science."
