When you’re facing hard problems, sometimes the best answer is to discard what you think you know to be true, and to think differently.
Three hundred years ago the Royal Navy and the British Merchant Marine were facing a very hard problem: How to determine a ship’s longitude on the high seas.
Let’s back up: If you know your latitude (north/south) and longitude (east/west), you know exactly where you are. When you’re onboard a ship out of sight of land for days or weeks, this is more than handy: It’s imperative. Latitude has always been relatively easy to determine, from the altitude of the sun at noon (with the aid of a table), but longitude was thorny. I knew a fair amount about the problem from having read the 2007 Dava Sobel book, Longitude, but it wasn’t until I was in London last week that I had the chance to visit the Royal Observatory in Greenwich and see first-hand some of the artifacts of the period. The genius it took to solve this hard problem—by thinking differently—is now blazed into my memory.
The Royal Observatory itself was founded by King Charles II in 1675 primarily to solve the longitude problem:
Whereas, in order to the finding out of the longtitude of places for perfecting navigation and astronomy, we have resolved to build a small observatory within Our Park at Greenwich…
Here’s a clear statement of the problem from the Royal Observatory’s own site:
For every 15° that one travels eastward, the local time moves one hour ahead. Similarly, travelling West, the local time moves back one hour for every 15° of longitude.
Therefore, if we know the local times at two points on Earth, we can use the difference between them to calculate how far apart those places are in longitude, east or west.
Theoretically, therefore, “all” one had to do was to provide ships at sea with clocks that could accurately tell the time at some reference point (say, Greenwich), compare it to local time, and presto. But 300 years ago, far far easier said than done.
