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A diver viewed from below who appears inside of Snell's window. Snell's window (also called Snell's circle [1] or optical man-hole [2]) is a phenomenon by which an underwater viewer sees everything above the surface through a cone of light of width of about 96 degrees. [3] This phenomenon is caused by refraction of light entering water, and is ...
English: Snell's window as seen through an underwater tunnel at the St. Louis Zoo. Caustics in the water are visible near the sun. The black line through the frame is a gasket between segments of the tunnel.
Name Image Year built Location & coordinates Class of Light [3] Focal height [3] NGA number [3] Admiralty number [3] Range nml [3]; Biển Sơn Lighthouse: Image: 1962: Nghi Sơn Thanh Hóa province
Through "Snell's window" (top), we see some of the scene above the water, including the handles of the ladder (right of center). The color-fringing of the light (top) and of the edge of Snell's window is due to variation of the refractive index, hence the critical angle, with wavelength. Reason I can't comment on its merits as a sports photo.
Martin Edge (op cit, p223) observes "I was once under the impression that the deeper you went the more [of snell's window] could be included [in the photograph]. This is incorrect! To photograph the full circle you need a fisheye lens equivalent to a 12mm lens on a 35mm format."
Mê Linh Square (Vietnamese: Công trường Mê Linh) is a city square next to the Saigon River in District 1, downtown Ho Chi Minh City, Vietnam.The square has a semi-circular shape and features a statue of Trần Hưng Đạo, it is separated from the Saigon River by the Bạch Đằng Quay.
Originally, many thước of varying lengths were in use in Vietnam, each used for different purposes. According to Hoàng Phê (1988), [1] the traditional system of units had at least two thước of different lengths before 1890, [2] the thước ta (lit. "our ruler") or thước mộc ("wooden ruler"), equal to 0.425 metres (1 ft 4.7 in), and the thước đo vải ("ruler for measuring ...
In Vietnam, the people played sáo when resting on the fields or before going to sleep at night. By the end of the 1970s, artists Đinh Thìn and Ngo Nam modernized the sáo by making this 6-finger-hole flute into 10-finger-hole flute, extending its register. [ 1 ]