Captain's Log

The earth's magnetic field changes. Sometimes it's weak, sometimes it's strong, sometimes north is south and south is north.

We know about these strange, not quite explicable, changes from more than 400 years' worth of ships' logs.

Presenter Simon Calder looks at these daily, detailed accounts of maritime voyagers. As they crossed the world's oceans, captains recorded weather conditions, the positions of stars and anything strange they saw along the way.

These logs supply valuable information for climatic and historical research, and give us a great picture of life on the high seas.

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