What is a compass?

Compass, also called Sina, is mainly composed of magnetic needles installed on the shaft. Under the action of natural geomagnetic field, the magnetic needle can rotate freely and keep in the tangent direction of magnetic meridian, and the north pole of the magnetic needle points to the geographical north pole, so the direction can be distinguished by this property. It is often used in navigation, geodesy, tourism and military affairs. The invention of the compass with physical direction indication consists of three parts, namely Sina, compass and magnetic needle, all of which belong to the invention of China. According to ancient mine records, it first appeared in the Cishan area during the Warring States Period. Compass is the result of China ancient working people's understanding of the magnetism of objects in long-term practice. As one of four great inventions of ancient china, its invention has played an inestimable role in the development of human science, technology and civilization. In ancient China, the compass was first used for rituals, etiquette, military affairs and divination, and to determine the orientation when looking at geomantic omen. 1 1 At the end of the century or at the beginning of the 2nd century, China ships began to use compasses for navigation. Zhou Ping can talk in the Northern Song Dynasty: "The shipowner (helmsman) knows geography, watches the stars at night, watches the sun by day, and watches the compass in the dark.

"Compass is an all-weather navigation tool applied to navigation, which makes up for the shortcomings of astronomical navigation and geographical navigation and opens a new era in the history of navigation. The introduction of Arabs into Europe created conditions for the navigation activities of later European navigators. Magnetic meridian changes with the seasons. First, on the vernal equinox and autumnal equinox, magnetic meridian coincides with the meridian and meridian of the earth, and the compass points directly to the north and south poles of the earth, with an error of only 0. The eccentricity of the earth axis can be ignored. Secondly, on the days of summer solstice and winter solstice, the magnetic meridian and meridian do not coincide, and the magnetic deflection angle is the largest, with the maximum deviation of plus or minus 23. 26, that is to say, the magnetic deflection point near the north and south poles of the earth is the largest. The circumference of the earth divided by the angle of 365 is plus or minus 23, which is equal to the distance between the magnetic deviation point and the north and south poles (plus or minus radian kilometers).

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