Recently my watch began reading time in a most bizarre
way. Someone told me it might be magnetized. What does this mean and how could it have
Oscar Peterson, Oxford, England
Answer by Professor J.C. Nicolet
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.
|A piece of magnetite found in the 17th Century which has been
enclosed in bronze. This natural magnet was placed in compasses used to navigate the high
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.)
|| Small iron filings demonstrate the lines of a magnetic field
surrounding a magnet.
Early preventive measures
In the 19th Century, the regulating organs of watches were made essentially of steel
thus making them highly susceptible to the effects of magnetic fields. The first measures
to prevent this problem consisted of placing pocket watches in empty waxed white iron
boxes which conducted the magnetic forces. While these waxed boxes were very efficient in
protecting the watches, their main drawback was that they had to be opened to tell the
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
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
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 on top of any of these items. Less obvious, but posing an even
greater danger for a gold watch are the magnets found in refrigerator doors or other
cabinets. Even a brief contact with these items is enough to magnetize a gold 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.