Scientists have long believed that animals use the Earth's magnetic field to direct migration pathways, but the mechanism has been a mystery. However, new research has identified cells in the nasal cavity of rainbow trout that act like tiny compasses.
Basic Optics and Optical Instruments by Naval Education Thorough coverage of theory and applications of optics examines optical glass, light, elements of mirrors, prisms and lenses, construction of instruments, maintenance and more. Discussions include ship telescopes and spyglasses, boresight telescopes, fixed prism gunsight telescopes, magnetic compasses, and many other subjects. Extensive appendixes include a glossary, symbols, and formulas.
Lo pan (or Luopan, trad Chinese 羅盤) is a Chinese magnetic compass, also known as a Feng Shui compass. It is used by a Feng Shui consultant to determine the precise direction of a structure or other item. It also can be displayed in an office or private home to avoid bad Feng Shui. Read more: http://www.formosa-art.com/feng-shui-tools/
To locate identical positions on opposite sides of a wall, we showed a method using a bar magnet and pocket compass in October 1943. The magnet, attached to a suction cup, holds the position on one side of the wall. On the other side, a compass points to the magnet so the spot can be marked.
Viking Sunstone, a rough, whitish block from an Elizabethan shipwreck, a crystal believed helped Vikings & medieval seafarers navigate high seas. Vikings, expert navigators, used the sun, stars, mountains & even migratory whales to guide them thru open water between Greenland, Iceland, and Newfoundland in today's Canada. Le Floch is one who suggested calcite crystals were used as navigation aids on long summer days with the sun hidden behind the clouds. Such crystals into the 16th century.