Some simple examples of diffraction, such as a pencil standing in a beaker of water and a coin placed on the bottom of a opaque bowl and water added until the coin again became visible, were used to define diffraction. Diffraction diagrams were drawn to show the normal ray, the incident ray, the angle of refraction, the refraction toward the normal when passing from less to more dense and the ray diagram to show refraction of light through a glass block.