Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of his Time
by Dava Sobel
Rating: 3.0 / 5 · Read · Finished 2026-02-14
Sailors can tell their latitude by the stars, but longitude is harder. You need to know the time back in the home port, and the time on your ship, and find the difference between them. Time on the ship is done by observing solar noon. Time back home is much harder. Spoiler alert: the solution ended up being a really accurate clock with lots of clever innovations to deal with various complications at sea.
The book is hailed as a super-accessible history mixed with science. I liked some parts but got bored for most of it. I guess I must not be into this style of book, because I didn’t like “About Time” either.
There are some great stories about how dangerous sea travel was before longitude was solved. For example, a ship knew it was on the right latitude but didn’t know if land was east or west. It sailed west for 3 days without finding land. All the while, sailors are dying of scurvy. Finally, they turn around and go east, 6 days and hit different land than they expected. Turns out they were just a couple hours from reaching their destination when they turned around :(
Interesting tidbits about astronomy. For example, you can use a lunar eclipse to tell what time it is back in your home port, because its time was predicted, and it’s visible everywhere simultaneously.
Also, I never understood this before, but the moon rises in the east AND the moon travels east. This is because the sky travels west (from our perspective) faster than the moon travels east.
Crazy stories about proposed and failed solutions to longitude including “the wounded dog” solution. Some people believed applying a particular substance to a bandage would both speed the wound’s healing and cause pain in the wound. Since this happens instantaneously, you can keep a wounded dog on your boat and soak the bandage back in the home port at noon each day. The yelp of the dog would tell you the time back home.
Once they finally had chronometers, they went chronometer-crazy. The HMS Beagle (carrying Darwin) had 22 chronometers.
A weird coincidence that will be easy to remember for Americans: Harrison (the inventor of the chronometer) died in 1776.