points or inches at the new range, the ranges are expressed in hundreds of yards. We are indebted to Major E. N. Johnson for this excellent formula. Illustrating the formula, for Springfield,

If the correction for 800 yards is 2.2 points, the correction for 1000 yards, the wind remaining the same is

The above formula is approximately true also for the Krag, or .30-220-2000, or 30/40.

STEVENS 425

Stevens .25-.30-.32-.35, High Power

For description,

see Vol. 11.

Stevens .22, Armory Model.

I'

CHAPTER XII.

Deflection Due to Rotation of the Earth.

Fa BODY free to move moves near or on the surface of the earth, the motion arising from the rotation of the earth apparently deflects the body to the right of its course in the northern hemisphere, and to the left of its course in the southern hemisphere. The body itself has not changed its direction, but the rotation of the earth has caused the surface of the earth to move from under the body, so that the object toward which the body was moving is shifted aside.

Several years ago we swung from the dome of the Masonic Temple in Chicago, the longest pendulum ever swung, to demonstrate the rotation of the earth, following the method, though greatly improved, of Foucault. As this pendulum swung from one side of the rotunda to the other it marked its position on the circumference of an 18 ft. circle. At each oscillation it apparently deviated to the right, about 8 inch, if the writer's memory is correct, although the pendulum constantly moved north and south in the same plane. The facts of the case were that the earth, the floor of the Temple and the circle were rotating beneath the pendulum, and they would have made a complete rotation in about 36 hours, i. e., in 24 hours divided by the sine of the latitude.

The angle of deflection, A, caused by the rotation of the earth is computed from the formula

in which A is the angle of deflection, in minutes, sine L the sine of the Latitude of the place, and T the time of flight in seconds.

The deflection in inches.

d = X X sin Ad

For. 39g

in which X is the range in feet, sin A found by formula 39f, and d the deflection in feet.

The deflection for the Springfield, .30-2700, 1500 yards. T-3.45 sec. is approximately 10 inches.

CHAPTER XIII.

Drift (So-Called), Deflection Due to the Rotation of the Projectile.

E

VERY rifle has grooves cut in its barrel spirally,

into which the projectile is forced by the pressure of the powder gases, and is thereby caused to rotate upon its longitudinal axis throughout its entire flight.

A projectile is a gyroscope and its great velocity of rotation causes its longer axis to assume to maintain a position parallel to the axis of the bore, throughout its entire trajectory curve, and it would do so if it were not for external forces acting upon it.

The longitudinal axis of a rapidly spinning top appears motionless, the same attitude is desired of a projectile in its flight.

When the projectile issues from the muzzle, if properly centered in the bore before it starts on its flight, its axis of rotation is tangent to the curve of the trajectory. But as soon as it starts on this curve gravity acting upon the projectile causes the tangent to deflect from the longer axis.

The resistance of the air always acts parallel to the tangent at any place along the curve. At first it is directly opposed to the forward motion of the projectile, but as soon as the tangent is inclined to the longer axis, Fig. 1. the resistance of the air tends to rotate the projectile backward over on its short axis, O, which is perpendicular to the plane of