Rotation as a Factor of Motion. 239 



resistance finally throws the ball to the right. If the ball had 

 balloted on the left side last, in leaving the muzzle, it would have 

 been deflected to the right by touch and afterwards to the left by 

 resistance and reaction of the compressed air. Thus it is possible 

 with a smooth-bored gun to " shoot round " a nearer object in 

 direct line and hit a more remote object behind it. 



I wish to give but one more instance of the effect of rotation 

 on direct motion. It is vulgarly called "curved ball." It may 

 be witnessed in any good base-ball match. The pitcher desires 

 to elude the strokes of the batter ; after delivering a few balls in 

 simple parabolic curves or with axial rotations, he will deliver the 

 ball from the hand in such a way that when the ball leaves the 

 hand the fingers touch it from below, causing the underside to be 

 retarded while the upperside moves forward. Then the ball ro- 

 tates upon a horizontal transverse axis, relative to its motion of 

 translation. The greatest resistance from compressed air is in 

 front and above the moving ball. The ball seeks a path of less 

 resistance, preserving its plane of rotation and drops enough to 

 form a depressed curve. By a skillful adjustment of rotation and 

 translation, the pitcher is able to produce about such g, curve as 

 he wishes. To the batter the ball seems coming toward a point 

 it is destined to fall short of. Again, by delivering the ball from 

 the hand with the fingers touching above, a backward rotation is 

 produced on the top of the ball and a forward motion to the under 

 side. Such a ball continues its course until accumulated resist- 

 ance of air from ahead and below throws it upward. So the 

 batter sees the ball coming toward a point it is destined to pass 

 clearly above. By skillful manipulation the right side of the de- 

 liverer the ball may be retarded, and the ball will^curve to the 

 right, and by retarding the left side it will curve to the left. The 

 amount of curvature is variously estimated by different persons. 

 With the rotation or twist of the best pitcher, it is no uncommon 

 thing to make a ball curve a yard from its direct path, while many 

 cannot effect any curve. 



This purports to be only the outline of a subject worthy of 

 much greater investigation, in its relation to great scientific prob- 

 lems. 



