This argues that the sportsman who closes one eye at the time of taking aim at an away-going bird, really has a very imperfect view of it—but half a picture, as it were—hence the aim could not possibly be so perfect as in case where the picture was rendered more distinct by the use of both eyes, in accordance with the clear explanation of Sir David, who goes on to state:
“But though we see with one eye the direction in which any object or point of an object is situated, we do not see its position or the distance from the eye at which it is placed. In monocular vision we learn from experience to estimate all distances, but particularly great ones, by various tests, which are called the criteria of distance, but it is only with both eyes that we can estimate with anything like accuracy the distance of objects not far from us.
“The most important advantage which we derive from the use of two eyes is to enable us to see distance, or a third dimension in space. That this vision is not the result of experience as monocular vision is, is obvious from the fact that distance is seen as perfectly by children as by adults; and it has been proved by naturalists that animals newly-born appreciate distance with the greatest correctness.”
Dougall’s Reasoning.—Mr. Dougall says, in his “Shooting Simplified,” that “A thorough good gun will knock over a hare running broadside, with four or five shots at seventy yards distance, but full elevation must be taken, and the gun fired with the head well raised and the eyes kept steady on the aim, not taking sight along the rib, with the eye well down behind the breech, as has been erroneously recommended.
“Distance requires elevation in proportion. A rifle is fitted with graduated sights to meet this, but the elevation of the rib of a fowling-piece is fixed and immovable. But by a simple law of perspective, when you look at a hare (or any other object) seventy yards away, bringing mechanically the sight to bear upon it, you have the breech of the gun lower than if it were only forty yards off; whereas, if you adopt the one-eye system, you fire at exactly the same elevation at all distances. It would be as absurd to take a level aim along the rib at seventy yards as it would be to fire a rifle at a mark at two hundred yards with the sight set for one hundred.
“While everything has been done to increase the range of the fowling-piece, nothing has been done to give the elevation necessary to take full advantage of the increase of power. As long as the one-eye system of shooting is adopted, the object, if hit at all, will be struck only by outside weak pellets, and not by the effective central shot.
“The proper way is to throw the gun well up and into the shoulder; the setting off of the stock will then bring the gun right in front of the face; and, the head being erect, and both eyes fixed intently on the object, the line of motion is commanded, and the aim taken instinctively. The central pellets have thus an allowance given them to compensate for distance and the motion of the object. You look along the imaginary line, higher at the breech according to distance, and at this elevation the gun is fired, exactly as a rifle target-shooter sets his breech sights to a given distance.
“How does a man drive a nail? Certainly not by closing one eye and looking along the hammer; but with both eyes open, he mechanically balances the hammer and strikes instinctively, never, if accustomed to the use of the tool, missing his aim. It is the same in shooting.”
Coming directly to the subject of employing binocular vision in taking aim to shoot, Mr. Dougall quotes from a paper in Once-a-Week to the effect that monocular vision, while much employed for this purpose, cannot at all be depended upon. To prove this position, place upon a table an empty small-mouthed vial, and taking another similar vial full of water in one hand, shut an eye and approach the vial upon the table; when apparently near enough, stretch out your arm quickly and endeavor to pour the water from the full vial into the other, still keeping the eye closed. You will be very apt to find, as the water comes down, that it is missing the mouth of the empty vial on account of a miscalculation, due to monocular vision. Now repeat the operation with both eyes open, and if care is exercised success will be the invariable result. A similar miscalculation will be shown to the person who endeavors to approach and snuff a candle with one eye shut.
Mr. Dougall thinks there can be no reasonable question as to the advantages of learning to use the shot-gun with both eyes open. This has been proven time and again by the most rigid tests. It is even a settled fact that the nearer the eyes of an individual set together in the head the less he is likely to shoot well. “And yet,” says Mr. Dougall, “how strange it is to find sportsmen who would still further narrow this fine provision of nature into the diameter of one retina only. Throwing the fowling-piece into a line with the object of aim by an instinctive effort, keeping both eyes firmly fixed on and following the flight of the object, is the first great principle in shooting well.”