Although ripple tanks have been used in the past to perform wave simulations for electromagnetic and acoustic phenomena, especially before the advent of computers, they are still often used to demonstrate wave propagation in high school and college physics classrooms. Usually ripple tanks have a rectangular shape. The wave propagating through the tank interacts with smaller slits, reflecting surfaces, and similar objects. Sophisticated circular ripple tanks have been built in the past, but their main purpose was for the study of wave phenomena in rotating systems. John Fleming in his book describes an elliptical ripple tank, but it is not clear if he actually built one. He discusses the possibility of generating a wave at one of the focal points of an ellipse and focusing it at the other.