concave area
51History of the telescope — The earliest known working telescopes appeared in 1608 and are credited to Hans Lippershey and Zacharias Janssen, spectacle makers in Middelburg, and Jacob Metius of Alkmaar. The design of these early refracting telescopes consisted of a convex… …
52Western architecture — Introduction history of Western architecture from prehistoric Mediterranean cultures to the present. The history of Western architecture is marked by a series of new solutions to structural problems. During the period from the… …
53Surface tension — For the work of fiction, see Surface Tension (short story). Surface tension is a property of the surface of a liquid that causes it to behave as an elastic sheet. It allows insects, such as the water strider (pond skater, UK), to walk on water.… …
54motion-picture technology — Introduction the means for the production and showing of motion pictures. It includes not only the motion picture camera and projector but also such technologies as those involved in recording sound, in editing both picture and sound, in… …
55Polar coordinate system — Points in the polar coordinate system with pole O and polar axis L. In green, the point with radial coordinate 3 and angular coordinate 60 …
56Elephant and mammoth ivory — Mammoth Ivory tusk carved by Japanese Master carver Elephant and mammoth tusk ivory comes from the two modified upper incisors of extant and extinct members of the order Proboscidea. Mammoths are believed to have been extinct for 10,000 years.… …
57Kerr-lens modelocking — (KLM) is a method of modelocking lasers via a nonlinear optical process known as the optical Kerr effect . This method allows the generation of pulses of light with a duration as short as a few femtoseconds.The optical Kerr effect is a process… …
58Schreger line — Schreger lines are visual artifacts that are evident in the cross sections of ivory. They are commonly referred to as cross hatchings, engine turnings, or stacked chevrons. Schreger lines can be divided into two categories. The easily seen lines… …
59Plough — Plow redirects here. For the Canadian soldier, see Edward Chester Plow. Plowman redirects here. For the surname, see Plowman (surname). Furrow redirects here. For other uses, see Furrow (disambiguation). For other uses, see Plough… …
60Satellite dish — A C band satellite dish …
