The Mariner's Compass

By the late sixteenth century, the mariner's compass had evolved into an instrument not very different from the compass of today.

In ancient times, the physical housing of the compass itself was typically made from wood or ivory. Later, brass came into use as the metal was much more durable than those softer materials and the non-ferrous properties of brass was confirmed to not affect the behavior of the magnetic needle.

The Pole Star (Polaris) served as the seaman's lodestar (or star that shows the way). Therefore the magnetic stone which was used to magnetize the compass needle was called a lodestone. The magnetic, direction-finding property of the lodestone had been discovered in China as early as the twelfth century.

By the sixteenth century, the design of the mariner's compass had evolved slightly.  The interior of the compass had replaced it's simple magnetized rod with a soft iron wire bent to a lozenge shape and attached to the underside of a circular compass card, which was suspended at the center on an upright needle.

Because the iron wire tended to lose its magnetism over a period of time, it was necessary for each ship to carry a good lodestone to re-magnetize the wire when it weakened.

Box CompassDespite the design improvements of the mariner's compass, it did have a significant flaw: The magnetized wire in the compass was drawn by large land masses. This caused the compass to have variations in its readings.

The mariners and mathematicians of this early period were concerned about this problem, and a number of corrective measures were tried. However, at the time the Mayflower sailed in 1620, the problem had not been satisfactorily solved.

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