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Winter Web: Activity 3: Visiting the Artic Circle: The Magnetic North Pole: Readiness Reading Activity

During the sixteenth century, mariners believed that somewhere in the North was a magnetic mountain that was the source of attraction for compasses, and, unfortunately, for any ships that strayed too close to it. It was not until 1600 that someone came up with a better idea. Sir William Gilbert, physician to Queen Elizabeth I, suggested that the Earth itself was a giant magnet and that the force that directed the compass originated inside the Earth. Using a model of the Earth made from lodestone (a naturally occurring magnetic rock), he also showed that there should be two points on the Earth where a magnetized needle would stand vertically at the North and South Magnetic Poles.

This is basically the same definition used today. At the magnetic poles, the Earth's magnetic field is perpendicular to the Earth's surface. Consequently, the angle between the horizon and the direction of the earth's magnetic field is 90°. And since the magnetic field is vertical, there is no force in a horizontal direction. Therefore, the angle between true geographic north and magnetic north cannot be determined at the magnetic poles.

Gilbert believed that the North Magnetic Pole coincided with the north geographic pole. Magnetic observations made by explorers in subsequent decades showed that this was not true, and by the early nineteenth century, the accumulated observations proved that the pole must be somewhere in Arctic Canada.

In 1829, Sir John Ross set out on a voyage to discover the Northwest Passage. His ship became trapped in ice off the northwest coast of Boothia Peninsula, where it was to remain for the next four years. Sir John's nephew, James Clark Ross, used the time to take magnetic observations along the Boothia coast. These convinced him that the pole was not far away, and in the spring of 1831 he set out to reach it. On June 1, 1831, at Cape Adelaide on the west coast of Boothia Peninsula, he measured a dip of 89° 59'. For all practical purposes, he had reached the North Magnetic Pole.

The next attempt to reach the North Magnetic Pole was made some 70 years later by the Norwegian explorer Roald Amundsen. In 1903 he left Norway on his famous voyage through the Northwest Passage, which, in fact, was his secondary objective. His primary goal was to set up a temporary magnetic observatory in the Arctic and to re-locate the North Magnetic Pole.

A pole position was next determined by Canadian government scientists shortly after World War II. Paul Serson and Jack Clark, of the Dominion Observatory, measured a dip of 89° 56' at Allen Lake on Prince of Wales Island. This, in conjunction with other observations made in the vicinity, showed that the pole had moved some 250 km northwest since the time of Amundsen's observations. Subsequent observations by Canadian government scientists in 1962, 1973, 1984, and most recently in 1994, showed that the general northwesterly motion of the pole is continuing, and that during this century it has moved on average 10 km per year .

Answer the following questions:

1. What can you tell about the location of the magnetic north pole in the 1600's as compared to the location today?

2. What is the magnetic north pole used for?

3. Where do you think the Dominion Observatory is located? What made you chose this location?

Use the internet to research the following explorers; then write a short biography of their life and include why they are important contributors to the magnetic north pole theory:

Sir William Gilbert

James Clark Ross

Roald Amundsen

Paul Serson

Jack Clark

Return to Winter Web Activity 3


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