Summary of Deviating Causes

—The following summary may be considered as embracing nearly all the causes of deviation of cannon and small-arm projectiles: 1st. From the construction of the piece. These causes are, wrong position of the sight; bore not of the true size; windage, etc. 2d. From the charge of powder. Improper weight; form of grain and variable quality of the powder, etc. 3d. From the projectile. Not of the exact size, shape, or weight; disfiguration in loading, or on leaving the bore; eccentricity. 4th. From the atmosphere , etc. The effect of wind; variations in the temperature, moisture, and density of the air; position of the sun as regards the effect on the aim; difference of level between the object and the piece; and rotation of the earth. It is found that a projectile will deviate to the right of the object in the northern hemisphere whatever may be the direction of the line of fire, and at a distance from it, depending on the latitude of the place, and on the time of flight and the range of the projectile.