Kelly Prime

And so for many, many years, longitude was just garbage as a real-world value.

One such depressingly bad method was called sailing the parallels, where ships could find one line of latitude and just stick to it until it was time to basically turn north or south off the highway.

This was a really popular approach, enough so that everyone started sailing along the same lines.

Another less bad way of estimating longitude was called dead reckoning, a way of measuring speed and direction.

How it worked is that you'd tie a series of knots in a rope and then throw that rope behind you in the water.

How quickly the knots fed out would tell you how fast you were going.

Having a general sense of speed could tell you how far you'd gone east or west.

But dead reckoning was notoriously inaccurate, especially on long journeys where even small errors could accumulate.

This is Deva Sobel, who wrote the best-selling book Longitude.

Having accurate coordinates at sea could mean the difference between making a swift, safe journey and, say, veering dangerously off course, hitting a rock, and drowning with a guy named Cloudsley.

But the search for longitude wasn't only about safety.

For Great Britain, it was also very clearly a matter of empire.

In the early 18th century, Britain had colonized parts of North America and the Caribbean, and they were actively growing the transatlantic slave trade.

Having longitude would mean shorter, more predictable journeys.

In other words, they'd be able to do more horrible things more quickly.

So, with global domination on the line, Parliament passed the Longitude Act of 1714.

The rules of the act were this.

If your idea passed muster with a board of qualified judges, you'd be sent on a trial journey to a place of known longitude.

In this case, Britain's colonies in the Caribbean, then known as the West Indies.

And there were different prizes depending on how close your ship got to the bullseye.