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
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Activity 3
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