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KF5JRV > TECH 13.09.19 12:04z 36 Lines 2257 Bytes #999 (0) @ WW
BID : 14362_KF5JRV
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Subj: Compasses
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The magnetic properties of magnetite, the lodestone used in compasses, have been known for thousands of years, but it was not u
ntil the 12th century that Chinese navigators began using the mineral in compasses to help sailors find magnetic north. Early c
ompasses consisted of a magnetized bar or needle floating in a dish of water. More advanced instruments placed the needle on a
pivot so it hovered above a card bearing a compass rose, whose points correlated to the Temple of the Winds devised by the anci
ent Greeks.
Compasses were popularized in the 15th century by Portuguese sailors, whose instruments sometimes featured magnetized cards tha
t pivoted rather than needles. Other compasses were designed to be read from below, say by a sailor laying in his bunk. By the
16th century, the world’s greatest European compass makers were based in Nuremberg and Bruges.
As navigation aids, compasses are certainly better than nothing, but they are not without their shortcomings. The first problem
is that magnetic north and true north are not the same, which means compasses had to be designed to compensate for the resulti
ng magnetic declination. The needles in compasses were also affected by the steel in ships, which was offset in the early 1800s
by Commander Matthew Flinders, who devised his Flinders bars.
And then there is the sea itself, which practically guarantees that a compasses will never be read at rest and perfectly horizo
ntal. To solve this problem, gimbals were devised to keep the compass constantly suspended; the compass was typically placed wi
thin a binnacle which housed the gimbal and supported other instruments. By the 20th century, this technology was improved upon
and adapted to automobiles, which were outfitted with compasses to help drivers find their way on unmarked roads.
73, Scott KF5JRV
Pmail: KF5JRV @ KF5JRV.#NWAR.AR.USA.NA
Email: KF5JRV@GMAIL.com
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