Figure 49 comprises 2 schematic illustrations of ocular tests. In each illustration a lens is represented by a flat circular shape of uniform thickness. The edge and top surface of the lens can be seen. In first illustration (labelled “a”) a ball is shown resting on the surface of the lens. The ball is labelled as having a “22 mm diameter”. Above the ball there is a vertical force arrow pointing down and touching the top surface of the ball. It is labelled “100N force on stationary ball”. In the second illustration (labelled “b”) the ball is shown in space above the lens. The ball is labelled as having a “22 mm diameter 43 g mass”. On the left side of the ball there is a vertical motion arrow pointing down. The arrow is labelled “speed of ball at impact = 5.1 ms -1 ”.