99% Invisible Where the F*** Are We?
206 snips
Mar 3, 2026 
Deva Sobel, author and historian who explains the long struggle to solve longitude. Kelly Prime, field reporter who brings shipwrecks and island wayfinding to life. They recount deadly naval disasters, the obsessive clockmaker who reinvented navigation, maritime trials of sea clocks, and Polynesian non‑instrument wayfinding using stars, birds and waves.
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Time Difference Equals Longitude
- Longitude can be found by comparing local time to a reference time: 1 hour difference equals 15 degrees longitude.
- That required a clock accurate enough to preserve home-port time across long voyages.
Technical Obstacles To Sea Clocks And Harrison's Fixes
- 18th-century clocks were too unreliable at sea due to motion, temperature, and gunky lubrication.
- Harrison solved lubrication with lignum vitae and temperature with complementary metals to stabilize timekeeping.
H1 Proved A Sea Clock Could Work
- Harrison built H1, a 75‑pound steampunk-like sea clock that proved timekeepers could correct a ship's course.
- On a Lisbon trial H1 caught the Orford 60 miles off course and corrected it, impressing the crew.
