E-Archive


Vol. 10
May Issue
Year 2009
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Off the Beaten Track


in Vol. 10 - May Issue - Year 2009
True North



First Chinese Magnetic Compass




The crew had been uneasy for several days, ever since word had spread through the ship that the needle was no longer pointing towards the Pole Star, as it should have. The captain was well aware that, in these conditions, even the smallest incident could provoke a violent reaction among his men, and he took extra care to appear unworried and to go about his duties in his usual way. Deep in his heart, though, he grew alarmed as each passing night confirmed that the needle was deviating from its correct position more and more. His ship had left the shores of Europe almost a month ago, heading straight towards the setting sun, and the survival of all aboard depended on a navigational instrument which now appeared to be malfunctioning. Unable to sleep, he gazed at the stars as he strolled the deck, pondering what to do.

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It seems that the magnetic compass was brought from China to Europe by Arab traders. The Chinese encyclopaedist Shen Kuo gave a clear written account of suspended magnetic compasses in 1088 AD. One of the first Europeans to describe this invention was an English monk called Alexander Neckham, who wrote about a mysterious needle which always pointed in the same direction when attached to a straw and floated in a bowl of water. In his book entitled De utensilibus, published in 1180, Neckham tells of how this device was in common use among seamen on the Mediterranean. The arrival of the compass had an enormous economic effect, for trading vessels were no longer limited to sailing only during the good weather season and could find their way even under cloudy skies by day and night. The number of commercial voyages increased dramatically and this in turn encouraged investors, leading to even more voyages.

It was thought that the needle always pointed towards the Pole Star, for reasons no one could explain. This worked well as long as ships covered relatively short distances, however, as the distances grew longer and longer, it was noticed that the needle did not always point in the expected direction. Tradition has it that this phenomenon was first noticed by Christopher Columbus during his crossing of the Atlantic, causing panic among his crew. When other captains reported similar instances, it was realized that something had to be done to ensure the reliability and profitability of long distance commercial voyages.
In 1581 an Englishman named Robert Norman carried out a series of experiments with magnetized and unmagnetized needles floating in a bowl and noticed that they dipped into the water at their northern end. What he had discovered was something called magnetic dip, the incline at an angle from the horizon by a compass needle. This is caused by the fact that Earth’s magnetic field does not run parallel to the planet’s surface. Norman did not suspect the existence of this magnetic field and consequently he could not know that there was a difference between true north and magnetic north. A needle would show true north only when the two lined up. Otherwise, depending on the position of the needle on the surface of the Earth, the needle would deviate by a greater or lesser degree.

That the Earth had a magnetic field which was in fact attracting the needles was demonstrated by another Englishman called William Gilbert, who published his findings in 1600 in a book entitled De Magnete. Gilbert was the personal physician to Queen Elizabeth I, but he was strongly interested in scientific experiments. For over eighteen years, he carried out tests with the lodestone, a naturally-occurring magnetite used to magnetize needles. In the end, he concluded that the Earth itself was magnetic and that this was causing the needles to align in a north-south direction.

Many years later, the terms North and South Magnetic Poles were coined to describe the two points where the Earth’s magnetic field lines converge. The North Magnetic Pole is located to the west of Ellesmere Island in Canada. It might surprise many people to learn that this pole is continually moving northwest and that the Canadian government monitors its exact position on a regular basis. During the twentieth century the North Magnetic Pole has moved by about 1100 kilometers, at a speed which has increased since 1970 from nine to forty-one kilometers per year. This means that, if it kept its present speed and direction, the North Magnetic Pole will be located in Siberia in about fifty years!

By Giovanni Gregorat, Contributing Editor MFN
& Sales Manager, Pometon Abrasives




Author: Giovanni Gregorat