"Well, we can prove that," went on Mr. Baker.
"How?"
"Easy money. Let's see. This windowsill will do."
From his pocket Mr. Baker produced three halves of English walnut shells, and a small black ball, about the size of a buck shot. It seemed to be made of rubber.
"Here's a little trick that will prove any one's eyesight," he said. "The eye doctors in New York use it to test any person who needs glasses. A doctor friend of mine gave me this."
"How do you work it?" asked Hynard, seemingly much interested.
"This way. I place these three shells on the windowsill, so. Then I put the little ball under one. Watch me closely. I move it quite fast, first putting it under one shell, then the other. Now, I stop and, Hynard, tell me which shell it's under! I don't believe you can, I think my young friend can do so."
"All right," agreed Hynard.
"Which shell is the ball under?" asked Mr. Baker, drawing back, and leaving the three shells in a row; they all looked alike, yet Roy was sure the ball was under the middle one.
"It's under there!" exclaimed Hynard, putting his finger on the end shell nearest Roy.