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Lodestone attracting some iron nails Lodestone in the Hall of Gems of the Smithsonian Lodestone attracting small bits of iron. Lodestones are naturally magnetized pieces of the mineral magnetite. [1] [2] They are naturally occurring magnets, which can attract iron. The property of magnetism was first discovered in antiquity through lodestones. [3]
The dry compass in China was a dry suspension compass, a wooden frame crafted in the shape of a turtle hung upside down by a board, with the lodestone sealed in by wax, and if rotated, the needle at the tail would always point in the northern cardinal direction. [47]
A modern military compass, with included sight device for aligning. A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north.
In 1929, May was appointed to the Admiralty Compass Observatory, being Superintendent of Gyro-compasses at Devonport from 1933 to 1936, Malta from 1936 to 1939, and Portsmouth from 1939 to 1942. From 1942 he was responsible for organising installation and services for gyro-compasses as well as for training.
A reconstruction of an early Chinese compass. A spoon made of lodestone, its handle pointing south, was mounted on a brass plate with astrological symbols. [1]The history of geomagnetism is concerned with the history of the study of Earth's magnetic field.
Descriptions of lodestone attracting iron were made in the Guanzi, Master Lu's Spring and Autumn Annals and Huainanzi. [32] [33] [34] The Chinese by the Han dynasty (202 BC – 220 AD) began using north–south oriented lodestone ladle-and-bowl shaped compasses for divination and geomancy and not yet for navigation.
A lodestone cut out of rock and floated in water returns to the same direction. Iron heated to white heat and cooled lying along a meridian also acquires magnetism. But stroking with other materials fails—he proved this with an experiment with 75 diamonds in front of witnesses. The best way to magnetize a compass (magnetized versorium).
To use the compass, the base plate is first levelled with the horizon and then pointed roughly to what the user believes to be north. The equatorial drum is then tilted in relation to this base according to the local latitude. The sights are then set using the local hour angle and the declination of whatever astronomical body is being used ...