Modern Magic: A Practical Treatise on the Art of Conjuring

The secret lies in the fact that the hole in the ball is not made straight from end to end, but curved, with an angle or break in the middle. (See Fig. 132.) So long as the rope is slack, it runs through easily enough, but as soon as it is drawn taut, and thus forced into a straight line, it is clipped by the opposite angles a, b, and c, creating an amount of friction which would support a much greater weight than that of the ball. The performer has, therefore, only to draw the rope taut when he desires the ball to remain stationary, and to slacken when he desires it to run down.