A bit of history
The
phenomenon of magnetism was first observed by the Greeks about 600 B.C.
The natural magnet Fe3O4 (a black ferrous oxide), called magnetite was
found in the province of Magnesia in Turkey. Around the 3rd Century
A.D., the Chinese used magnetic material found in nature to make their
compasses so necessary in navigating the high seas. In 1600, William
Gilbert, physician to England's Queen Elizabeth I, published a treatise
called "De Magnete" which theorized that the earth was one gigantic
magnet, thus explaining variations in the movement of needles that had
been magnetized.
Artificial magnetism
Magnetic
fields produced by natural magnets are too weak to disturb the
operation of a watch. The same is not true, however, of man-made
magnetic fields. In the early 19th Century, when scientists discovered
how to produce very large electric currents, strong magnetic fields
appeared by electromagnetic inductance. This important physical
phenomenon was discovered in 1831 by Faraday, and began the development
of important practical applications of electricity, i.e. electric
motors, current generators, telegraph, telephone, radios, etc. In 1872,
Siemens produced the first really efficient electric motors, and over
the next 30 years, these new inventions quickly found their way into
small workshops wherever electricity was available.
By
the end of the 19th Century, the widespread use of electric motors
brought with it the widespread magnetization of pocket watches. The
first "victims" of this artificial magnetism were people employed in
factories using electricity. The early current generators caused the
formation of strong magnetic fields which had a negative effect on any
watches worn in the workplace.
A
solution to this problem arrived in the form of an apparatus composed
of a horseshoe-shaped magnet that could be turned by means of a crank.
At each half-turn, the polarity of the magnetism at any given point
changed direction. By alternatively moving the magnetized object towards
the horseshoe and then away from it, the article could be demagnetized.
(This same principle is used today except that the horseshoe has been
replaced by a powerful coil connected to an alternating current.)
Early preventive measures
The
first quarter of the 20th Century brought about significant changes in
this domain. The 1920 Nobel prize winner, Charles-Edouard Guillaume of
Fleurier, Switzerland invented a nickel-iron alloy which replaced the
earlier steel alloy in making balance springs. This greatly improved the
reliability of watches for three reasons:
· They were less sensitive to magnetism.
· They were less sensitive to rust due to humidity.
· They were less sensitive to thermal changes (which was the principal aim of Guillaume's research).
With
this alloy and the invention of stainless steel used in making cases,
watches were no longer susceptible to the effects of magnetism in the
home or in normal industrial workplaces.
And gold?
Unlike
their steel cousins, watch cases made from gold do not protect the
watch from the effects of magnetism. It is therefore advisable to equip
the movements of these timekeepers with a para-magnetic screen made of
iron, mu-metal or permalloy. This precaution is usually not taken for
esthetic reasons. A gold watch with a protective screen is not very
elegant, making it more difficult to sell. Perhaps one day,
manufacturers will look more closely at this problem. In the meantime,
wearers of gold watches should be careful not to expose their timepieces
to magnetic fields.
Magnetic fields in the home
So
where are the risks of these forces in the home? Non-negligible
magnetic fields are found near loudspeakers, stereo systems, televisions
and radios. Therefore, one should avoid setting a gold watch or any watches on top of
any of these items. Less obvious, but posing an even greater danger for a
watch are the magnets found in refrigerator doors or other
cabinets. Even a brief contact with these items is enough to magnetize a
watch. Caution is the byword when wearing one of these timekeepers
in the kitchen. Although a magnetized watch can be demagnetized as
mentioned above, the procedure is tedious. To do a good job, the watch
must be dismantled and each steel part demagnetized separately.