Dr Collins, who is both a physicist and a keen amateur cricketer, said that although he understood the theory, 'I've never been very good at making it work in practice'. The principles hardly differ, he said, from those behind the accepted practice of polishing one side of the ball and leaving the other in its naturally rough state.
Because air flows more smoothly over the polished side of the ball, that will tend to move faster, and so the ball will curve in flight towards the rough side, Dr Collins said. 'But the extent to which it does this depends on the ball's velocity and density of the air.'
Fast bowlers are too fast for polishing to have any effect, he continued. However, with medium- fast bowling the ball will slow in flight until, close to the batsman, it reaches a speed where the effect kicks in and the ball appears to swing just as the batsman is preparing his stroke. The ball will swing more when the air is damp.
The rules accept that bowlers should be able to affect the flight of the ball by polishing one side and leaving the other rough. Gouging simply makes one side artificially more rough than it becomes in the course of the game, and so accentuates the swing to the unpolished side, according to Dr Collins.
But he noted that everything depended on how the bowler kept the seam vertical and the degree of spin he put on the ball. Although many people have tried to research the flight of cricket balls using bowling machines, getting the ball to move in a desired direction is trial and error. It is conceivable, he said, that 'if any bowler had discovered by trial and error how to make gouging work, no one else will rapidly pick it up'.