"Water," said Jack.
"Right again!" said Ned. "And water does what to fire?"
"Puts it out," said Jack.
"Exactly so," said Ned. "And there you have it—action and reaction. That's the principle."
I think Ned borrowed his style of explanation not so much from the school-master as from a young man who appeared in the streets one day, selling a sort of stuff to clean the teeth, calling a crowd around him, and trying it on the teeth of one or two boys.
"That's all true," said Jack; "but how do you apply it to lightning-rods?"
"Here is a picture," said Ned, "of a house with a rod on it. The family think it's all right, and don't feel afraid when it thunders. But that rod may be broken somewhere, or may be rusted in the joints, and they not know it. What then? We simply fasten a large ball of ice—marked I in the illustration—to the rod at R—freeze it on tight. You see it isn't likely there will be any break, or any rusty joint, between the point of the rod and the ball."
"Not likely," said Jack.
"But there may be one lower down."
"There may be," said Jack; "though there couldn't be one higher down."