“Look through it, uncle.”
“Nothing of the kind, sir, you do not.”
Tom looked puzzled. What did his uncle mean? He had, he thought, looked through a pair of field-glasses scores of times at home in the old days.
“I make you stare, my lad, but I am glad to see it, for it shows me how right I am, and that you do think as everybody else does who has not studied optics, that you look through a glass at an object.”
Tom stared harder, and once more the old idea came to him, and he asked himself whether there were times when his uncle did not quite understand what he was saying.
“But you do, uncle,” he cried at last. Then he qualified this declaration by saying, “Don’t you?”
“No, my boy, once for all you do not; and if you take up any telescope, and remove the eye-piece before looking along the tube, you will see that your eyes will not penetrate the glass at the end. Then if you try the eye-piece alone, you will find that you cannot even look through that. How much less then will you be able to look through both at once.”
“But it seems so strange, uncle. You have a big magnifying-glass in a tube, and don’t look through it? Then what do you do?”
“Certainly not look through it, my boy.”
“But the bigger the glasses are the more they magnify—the moon, say.”