Place a pencil in a glass filled with water and what do you notice? Play this game to review Optics. Light is refracted differently through oil than water, which is why the results are more dramatic with a glass filled with half oil and half water. You can see this effect by putting a pencil in a glass of water. As a result, the image of the pencil appears to be broken or bent. The reciprocal action between the molecules of reflexion and t iii r»jiii i«i t refraction of various substances and those ot the ether which pervades ]i