Therefore, if you shot on a warm day and made 5's, and recorded temperature and other conditions in your score-book, you would know on looking at your score sheets that you should raise your elevation, if you were firing on a cold day.
[1398]. Effect of moisture. Dampness causes shots to strike high and dryness causes them to strike low. Therefore, on damp days take lower elevations than on dry days.
[1399]. Effect of light. Light affects the aiming without the beginner knowing it. It does not, however, affect the travel of the bullet.
A dark target causes a tendency to aim farther below the bull's-eye than if the target were bright. Therefore, use higher elevations with dark targets. As it gets darker, higher elevations should be used.
If you always aim carefully and correctly the light will have little effect on your aiming,—that is, if your eyesight is good.
If you are shooting in a dull light and a bright sun comes out, say on your right, there is a tendency to move the front sight to the opposite (left) side of the rear sight notch, since the near (right) edge is shaded and obscured somewhat. Therefore 1/4 to 1/2 windage into the sun (right in this case) should be taken to overcome this.
In using battle sight, hold higher for a bright light.
We also raise our sights if a strong sun comes out. Therefore, we have this rule: Move your rear sight into the sun, just as you do for a wind,—and raise your elevation.
[1400]. Mirage gives a wavering appearance to the target. It is heated air that is moving. It is sometimes called "heat waves."
With the wind between 2 and 14 miles an hour on clear, hot days the waves can be seen moving across the target.