Which 18th-century invention finally solved the 'longitude problem' for maritime navigation, allowing sailors to accurately determine their east-west position at sea?

Before GPS and modern navigation systems, sailors relied on various instruments to find their way across vast oceans. In the 18th century, one particular invention solved a critical problem that had plagued maritime navigation for centuries. This device was so important that the British Parliament offered a substantial reward for its creation. Test your knowledge about this revolutionary maritime invention that transformed sea travel and saved countless lives.

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Harrison's Marine Chronometer (H4)
Hadley's Reflecting Octant
Franklin's Gulf Stream Chart
Cook's Lunar Distance Tables