SOME HISTORY

Evening Post, Volume CXVI, Issue 103, 28 October 1933, Page 26

SOME HISTORY

THE MARINER'S COMPASS

Tho uiariucr's compass is nn instrument- designed to utilise ' the earth's magnetism for purposes of navigation, writes W. H. •Phillips.' According to the Chinese history the compass was first used by them in cars and carriages as a guide for them across the Great Plains of Tartury, a region in Central Asia. There is no genuine record, however, of a Chinese1 marine compass] before 1300 A.D. although there is positive evidence that the Chinese knew the power of a lodestone as early as 121 A.D. Towards the end of the thirteenth century compasses-of some form or other seemed to have been in general use by all maritime nations. - The:card or dial made to'turn with, tho needles is supposed to have been added, in the fourteenth century. In 1391 the Poet Chaucer mentioned the thirty-two points." The earliest mention of gimbals was about 1600 A.D. In 1813 the. liquid compass was invented by an Englishman, Francis Crow, and although various other forma have- been invented and used this liquid, compass, with, improvements of detail, is the most popular form in use today. The standard diagram of. the com-pass-dial coifSists. 'of an outer ling marked in degrees from tte aoi'tji £9*s*,

continuously to the right for 360 degrees. There is also placed inside of this degree diagram a magnetic diagram marked to quarter points. The old style ,of compass consisted of a dial containing tho magnetised needle balance on a pivot in a spun brass bowl with a top of glass on it. With tho coming of power propulsion this style became impracticable as the vibration of the engine caused the'dial to oscillate so continuously that steering a compass course became increasingly difficult and often impossible. In order to steady the action of the dial it was found necessary to employ a liquid. There are two varieties of this instrument —Chedwynd's "Spirit" compass and Kelvin's "Oil" compass. The liquid portion of tho former (which is the older), consists of thrcofiftlis of water and the remainder of alcohol. The oil compass is rilled with a colourless mineral Oil, which, in addition to being lighter than the spirits, will not freeze.