To increase the amount of light collected by the objective lens of a microscope, a technique known as oil immersion microscopy is used. To replace the air between the objective lens and the thin slip of glass (n = 1.51) covering the specimen, a drop of oil with the same index of refraction as the cover slip fills the space between them. Using Snell's law, sketch some light rays from the specimen to the objective lens in both cases and explain why this technique is useful.