ESTIMATING DISTANCES.
The light, the state of the atmosphere, and the nature of the ground are the chief disturbing causes in estimating distances and admit of no rules.
The sun on one's back, a light background, water or snow to look over, ground that is uniform and offers no prominent points of reference, or when the air is particularly clear, as after a rain, tend to make objects appear near.
A dark background, the sun in one's eyes, undulating ground to look over, or when it is cut by ravines or covered by trees or dwellings, or seen dimly at evening and in misty weather, tend to make objects appear distant.
In estimating distance under the usual conditions:
Men's features can be distinguished at 300 yards, head-dress at 600 yards, movement of legs and arms at 1000 yards.
Infantry can readily be distinguished from cavalry at 1200 yards.
Individual men become vertical lines at 1500 yards.
Distinguishing between infantry and cavalry only by mode of motion at 1500 yards.
A mounted man looks like a speck or dot at 2000 yards.
One can perceive men and horses at 2200 yards.
One can count the windows of a house at 4300 yards.
By day the glittering of the sun upon the arms of troops in motion indicates the direction of their march. If the rays are perpendicular, they are moving directly toward you; if slanting from left to right downwards, they are moving towards your right, and vice versa; if the rays are intermittent and varied, they are moving away from you.
Dust raised by cavalry forms a high light cloud, by infantry a lower and denser one, by wheeled vehicles denser still.