CHAPTER IVA LESSON IN OBSERVATION
The strenuous work was completed before night covered the scene. The flying machines had acted as a screen, and the guns, now in position, were effectually covered from the eyes of a prying foe. As they were about to leave the captain said:
"For the present you may find room in the vans, but tomorrow the regular quarters will be prepared near the guns."
The steaming hot supper, which was brought up in the kitchen vans, was relished as never before. After the meal they sat around and talked over the incidents of the day, and learned each other's histories, for there is a comradeship in the field that obtains nowhere else in any other occupation.
"And so you have been flying?" said the sergeant. "That has always had a fascination for me, but, strange as it may seem, I have never yet been up in the air, although I have had many opportunities. I have often wondered how things look from a height of two kilometers."
"Well, the first time I went up I couldn't distinguish a thing," said Ralph. "I could tell whattrees were, and could make out rivers, and houses, of course, but outside of that everything else looked like a blurred picture."
"Couldn't you make out people walking, or troops marching, and the like?" asked one of the men.
"No, indeed," said Alfred. "Why, how big do you suppose a man would look at a distance of five thousand feet, when you are directly overhead?"
"I don't know," replied the sergeant, with an inquiring look. "I don't suppose he could be seen at all, unless he happened to be moving."
"Why, at that distance it would be impossible to see the man, moving or not, for he would not appear bigger to the eye than the end of the finest wire," Ralph informed him.
"I remember when we made our first flights at Bar-le-Duc, that the lieutenant asked us to give him our impression as to the sizes of objects we saw and to tell him what they were. When a fellow is flying about the first thing he will notice is a river, if there is one anywhere in the neighborhood, and, of course, I saw a bridge. I couldn't wait until we landed before I marked it down on a piece of paper: 'A bridge; 200 feet long.' I thought I'd get it long enough. We were then flying about 5,000 feet above the earth. I saw the lieutenant smile. At that height the bridge looked about like a lead pencil held ten feet from the eye. Well, when we landed, the lieutenant said: 'It was a bridge, sure enough, but it happens to be seven hundred feet long.'"
"That reminds me," observed Alfred, "that we talked about several other things on that trip, and it will show how poor the judgment is unless the eye is well trained. Do you remember the drill ground east of Fleury? Well, we were asked to put down the number of men we could estimate in each group, and I was particularly anxious to tell the lieutenant how many men were in each of the squares which were formed. Each block of men, as they appeared to me, were about the size of a domino. I felt sure there couldn't be more than 50 men, but the lieutenant said there were at least two hundred."
"But that isn't the worst of it," rejoined Ralph. "We knew they were soldiers, because they were on the drill ground, but if that same number of men had been in the open country, it would have taken an expert to see them. I was fooled in that way not long after the experience I was just telling about, and, although the lieutenant pointed out the marching men, I couldn't spot them until he told me to watch for the glint of steel that would occasionally flash out. Then I understood."
"I have heard it said that if every moving object, it mattered not how big it might be, were painted the same color as the earth and other surrounding objects, aviators would not be able to discover them; is that really so?" inquired the sergeant.
"Yes," answered Ralph. "I think it's pretty near the truth. Sometimes even the upturned face of a man will attract attention, although the facemakes a mighty small speck, but I believe that fellows who think they can see a man's face at a distance of 5,000 feet, either use a field glass, or the man below happened to be wearing eye glasses, for they make fine reflectors for the airmen."
"But those who are flying get birds' eyes, after a time," said Alfred.
"What is that?" asked the captain, who appeared at the door. "Do you think a man's eyesight grows keener by flying, after he is at it for a time?"
"It seems so to me," answered Ralph.
The captain shook his head. "I think that is a misapprehension. The eyesight does not become sharper or more acute."
"Then how is it that I can now see things that I could not notice when we first began to fly?" asked Alfred.
"Observation! observation, my boy! You can't see one whit better today than you could the first time you went aloft," said the captain. "The eye is a very deceptive thing,—you laugh at the statement,—well, I'm going to prove it. In everything you see the judgment is not formed by what the eye tells you, but by your knowledge, your habit of observation and application growing out of previous experiences."
"Pardon me, Captain. Do you mean to say that the eye doesn't correctly tell you distance or size or what the object really is?" asked Alfred.
"That's exactly what I mean," replied the captain.
"Well, that's a new idea to me," said Ralph.
"Suppose we examine that. I have an article here,—a box, in my hand. Tell me, Ralph, how large it is, what it is made of, and what it is used for?" said the captain.
"Quite easy," replied the boy. "It is about two inches long; is made of metal, of some kind, and is used to hold matches."
"The answer needs examination. Now, tell me, first, how you judged it to be two inches long," remarked the captain.
"Why, I should easily judge that, because it wasn't as big as your hand, and not even as long as one of your fingers," said Ralph.
"In other words, you used my hand to measure it by, or, if my hand hadn't been there you would have guessed its size because you knew, approximately, the size of match boxes; is that it?" asked the captain.
"Yes," was the answer.
"Very well; how did you know it was of metal?" was the next question.
There was a broad grin on the faces of all; that was too easy; Ralph's face was all aglow as he answered: "Because I know that all match boxes are made of metal, and it looked like metal."
"You mean it was your previous knowledge; that is a fair answer," replied the captain. "But how did you know its uses?"
Ralph glanced about preparatory to making the answer, and Alfred replied: "I should say because I know that a box of that kind and of that size, andI've seen hundreds of them, is used for holding matches."
"Well answered. Now, let us sum up: the eye told you that the box was about two inches long. That is fairly accurate. You got the measurement simply by comparison. If a box had been placed within the range of your vision, so that there would be absolutely nothing with which to compare it, you could not have told by a mere observation of the eye whether it was an inch or three inches long," observed the captain.
"Do you mean I wouldn't have been able to tell the size of a match safe?" asked Alfred.
"No; I didn't say match safe. I said ifa boxhad been exhibited before you. If I had asked you the size of a match safe it wouldn't have been necessary for me to exhibit it; your knowledge of the general sizes of match safes would have enabled you to answer me without even glancing at it. Isn't that true?" asked the captain.
"I see what you mean now," said Ralph. "It is previous knowledge that aids the eye."
"That is the idea," said the captain. "Now, proceed with the next question. Why did you say it was made of metal?"
"Because I never saw a match safe that wasn't made of some kind of metal," said Ralph.
"Did the eye tell the truth?" said the captain, taking out his knife and opening it. "You will see it is made ofpapier mache, merely colored to look like metal. The eye was a gay deceiver; don't you think so?"
This was too much for the men; there was a sally of laughter in which the boys joined with the greatest glee.
"But we are not through with this investigation. We have been talking about a match safe. The sergeant here is a very wise person, and has had a fine education, so I am going to ask him whether it looks like a match safe," said the captain.
"I should say so; that is about the only thing that occurs to me," he answered.
"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 dependon 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."