"Are you relying on your eyes, or what?" asked the captain.
"Well,—on my eyes and on my previous knowledge," answered the sergeant.
"Then you are doubly wrong," said the captain, as he opened the lid, and exposed the interior of the case filled with tablets. "It is not a match safe; was never intended for one, and was never used for that purpose. Have I proven my case?"
The company applauded the clever manner in which the captain explained the subject.
"This leads me to say that the eye brings into your range something which may be familiar, that is, something of which you have seen before, and you say you have seen thus and so; or, on the other hand, you see something which is unknown, or strange. It is at this point where the value of observation is of service. If you cannot compare its size with something you have knowledge of, or have no gauge by which you can determine of what it is made, and no means which will enable you to judge of its use, or its purpose, you must depend on your own judgment to decide what it can possibly be. In course of time the man in an airship becomes a thinker and a reasoner, and does not depend so much on the eye, as upon a judgment aside from that which the eye tells him. Do you understand now what I mean when I say that the eye does not grow more acute, but that the mind becomes more active, and, through observation, enables the aviator to judge more accurately as time goes on."
The captain's argument was unanswerable. It was a revelation to the boys, and, as the captain was about to leave, Ralph said: "We thank you, Captain, for the wonderful lesson you have taught us. I am sure we shall never forget it, and I know we shall profit by it."
CHAPTER V
THE CURTAIN OF FIRE
Before the morning sun had lighted up the scene, they could hear the buzzing of airplanes overhead. That was a sound so familiar to them that they could, at times, distinguish even the motors that were used on most of them.