Water, 15. Stephenson, George, 63, 375. Stop, in lens, 244; iris, 249; use of, 48. Focus, meaning of, 325; simple, _328_; wheel, _327_. Beau de Rochas, 89. Bell, diving, _332_; electric, 119, _120_. Bellows of organ, 298. Pelton wheel, _377_.