With his pencil he drew a diagram, being always ready to draw maps and plans of all kinds. He drew it on the back of a card that chanced to lie on the table.
“There, that long straight stroke, that’s the line of the gun—it’s three inches long—now, see, put A at the top, and B at the bottom like they do in geometry. Now make a dot C on the line just an inch above B. Now suppose B is where the stock touches your shoulder, and this dot C is where your hand holds the gun in our old way at home. Then, don’t you see, the very least mistake at C, ever so little, increases at A—ratio is the right word, increases in rapid ratio, and by the time the shot gets to the bird it’s half a yard one side.”
“I see,” said Mark. “Now do the other.”
“Rub out the dot at C,” said Bevis. “I haven’t got any indiarubber, you suppose it’s rubbed out: now put the dot, two inches above B, and only one inch from the top of the gun at A. That’s how he held it with his hand at this dot, say D.”
“I think he did,” said the governor.
“Now you think,” said Bevis. “It takes quite a sweep, quite a movement to make the top A incline much out of the perpendicular. I mean if the pivot, that’s your hand, is at D a little mistake does not increase anything like so rapidly. So its much more easy to shoot straight quick.”
They considered this some while till they got to understand it. All the time Bevis’s mind was working to try and find a better illustration, and at last he snatched up the governor’s walking-stick. The knob or handle he held in his right hand, and that represented the butt of the gun which is pressed against the shoulder. His right hand he rested on the table, keeping it still as the shoulder would be still. Then he took the stick with the thumb and finger of his left hand about one third of the length of the stick up. That was about the place where a gun would be held in the ordinary way.
“Now look,” he said, and keeping his right hand firm, he moved his left an inch or so aside. The inch at his hand increased to three or four at the point of the stick. This initial error in the aim would go on increasing till at forty yards the widest spread of shot would miss the mark.
“And now this way,” said Bevis. He slipped his left hand up the stick to within seven or eight inches of the point. This represented the new position. A small error here—or lateral motion of the hand—only produced a small divergence. The muzzle, the top of the stick, only varied from the straight line the amount of the actual movement of the left hand. In the former case a slight error of the hand multiplied itself at the muzzle. This convinced them.
“How we shall shoot!” said Mark. “We shall beat Jack hollow!”