P. S.—I am eleven years old, and live eleven miles from a school. I have gained my education from reading St. Nicholas, and studying at home.
Buffalo, N. Y.
Dear St. Nicholas: In your February issue, there was a communication concerning "curve-pitching," and a diagram was used to explain why a ball curves in a certain direction.
I beg leave to call attention to what I believe to be a mistake in the explanation. The writer says that the curve must be "toward the retarded side." I think it must be from the retarded side; for, the ball while advancing is also revolving in a horizontal plane,—we will say from right to left.
In its rapid flight, the ball condenses the air in front and tends to form a vacuum behind, and the condensed air in front attempts to flow around the sides of the ball to fill the vacuum behind.
Now, in the diagram mentioned, the side B, the rotation of which conspires with the motion of translation, resists, by friction, the attempt of the air to flow back; while the side D, in which the motion of rotation is opposite to the motion of translation, offers no resistance to the air in flowing around its side. For that reason the ball meets with most resistance in front of B, and least in front of D. Hence, taking the direction of least resistance, it curves toward D or from the side of most resistance.
Very respectfully,
Elmer Storr.