ILLUSTRATIONS OF ROBINS’ THEORY OF ROTATION.
With ball and double string.
1st Illustration. A wooden ball 41⁄2 inches in diameter suspended by a double string, nine feet long. It will be found that if this ball receive a spinning motion by the untwisting of the string it will remain stationary. If it be made to vibrate, it will continue to do so in the same vertical plane. But if it be made to spin while it vibrates it will be deflected to that side on which the whirl combines with the progressive motion.
By firing through screens.
2nd Illustration. By firing through screens of thin paper placed parallel to each other, at equal distances, the deflection or track of bullets can easily be investigated. It will be found that the amount of deflection is wholly disproportioned to the increased distance of the screens.
Bent muzzle.
3rd Illustration. To give further light upon this subject, Mr. Robins took a barrel and bent it at about three or four inches from the muzzle to the left, the bend making an angle of 3° or 4° with the axis of the piece.
By firing at screens it was found that although the ball passed through the first screens to the left, it struck the butt to the right of the vertical plane on which aim was taken in line of the axis of the unbent portion of the barrel. This was caused by the friction of the ball on the right side of the bent part of the muzzle, causing the ball to spin from left to right.