Not knowing longitude at sea cost thousands of lives across centuries

Sobel opens by establishing the staggering human cost of the longitude problem: without a reliable method to determine east-west position at sea, ships regularly miscalculated their location by hundreds of miles, running aground on rocks or reefs they believed were still far away, or missing ports entirely and running out of food and water on unexpectedly prolonged voyages. She recounts the 1707 disaster in which four British naval ships wrecked off the Isles of Scilly due to navigational error, killing an estimated 1,400 to 2,000 sailors in a single catastrophe.

This disaster, among others, directly spurred the British Parliament to pass the Longitude Act of 1714, offering a prize of up to £20,000 — an enormous sum at the time — to anyone who could devise a method accurate enough for practical navigation. Sobel uses this backdrop to establish why the problem mattered so urgently beyond mere scientific curiosity.

Takeaway: some of history's greatest technical breakthroughs were driven not by abstract curiosity but by staggering, ongoing human loss.