History Of the Compass
By 500 B.C., it was known that lodestone, a naturally occurring form of iron oxide also known as magnetite, had the ability to attract iron. No one knows where or when it was first noticed that a freely moving piece of lodestone tended to align itself so that it was pointing North and South. Written records indicate that the Chinese used magnetic compasses by 1100 A.D., western Europeans and Arabs by 1200 A.D., and Scandinavians by 1300 A.D.
Early compasses consisted of a piece of lodestone on a piece of wood, a cork, or a reed floating in a bowl of water. Somewhat later, a needle of lodestone was pivoted on a pin fixed to the bottom of a bowl of water. By the thirteenth century, a card marked with directions was added to the compass. By the middle of the sixteenth century, the bowl of water was suspended in gimbals, which allowed the compass to remain level while being used aboard a ship being tossed by the ocean.
In 1745, the English inventor Gowin Knight developed a method for magnetizing steel for long periods of time. This allowed needles of magnetized steel to replace needles of lodestone. During the early nineteenth century, iron and steel began to be used extensively in shipbuilding. This caused distortions in the operation of magnetic compasses. In 1837, the British Admiralty set up a special commission to study the problem. By 1840, a new compass design using four needles was so successful at overcoming this difficulty that it was soon adopted by navies around the world.
Until the middle of the nineteenth century, navigators used both dry-card compasses, in which the needle pivoted in air, and liquid compasses, in which the needle pivoted in water or another liquid. Dry-card compasses were easily disturbed by shocks and vibrations, while liquid compasses tended to leak and were difficult to repair. In 1862, improvements in the design of liquid compasses quickly made the dry-card compass obsolete for naval use. By World War 1, the British Army used liquid compasses on land, and liquid compasses are still the standard for the best hand held magnetic compasses.
Parts of a Compass
Know the following parts of the compass and their purpose.
a. Lubbers line
b. Needle
c. Housing
d. Compass card
e. Gimbals
f. Bowl