This is a delightful little gem for what it is. It’s the story of one man’s obsessive development of accurate timekeeping devices over decades, with the goal of properly measuring longitude from ships at sea. Recall that measuring latitude (position north/south) is relatively easy: find the north star and … um … do a bunch of things with it that I imagine mariners already know but I do not. Measuring longitude, on the other hand, requires accurately measuring time: leave London (for instance) with two clocks synchronized — one on shore and one on the boat. When you’re off at sea, register the moment when the sun is directly overhead; that’s noon. Your clock says that it’s 3pm back in London. So London is three hours ahead. So you’re 3/24ths of the way around the globe. The problem, then, reduces to accurately computing the time, in the presence of varying temperature, salt water, and rolling seas.

An alternative is to use detailed astronomical measurements. If you can discern patterns, say, in the relative movement of astronomical bodies — e.g., “on July 3rd at 8:35pm, the moon is 3 degrees from Venus in London, and every degree of longitude changes that relative position by a tenth of a degree” — you can write these down in astronomical tables, which sailors can carry with them around the globe. This method has obvious downsides, including mathematical complexity and the fact that clouds exist. It seems obvious, from this vantage point a couple hundred years on, that measuring time with a simple clock would solve both problems. At the time, though, decades of research had gone into the stargazing method of measuring longitude, and the British government’s longitude-measuring prize was granted by a committee that included men whose careers were based on the stargazing method. This is a conflict of interest, we’d say today.

The book is a nice 30,000-foot view of the varying approaches to measuring longitude, but it rarely dips below that altitude. We learn, for instance, that one of our hero clockmaker’s innovations was the bimetallic strip that lives on in modern thermostats. One of the metals expands when the ambient temperature rises; another of the metals contracts. The overall change in the metal is either zero, or consistent enough that its effects can be controlled in the rest of the device.

But what exactly is this strip doing? And how, fundamentally, does a clock work? I understand that there’s a spring somewhere. I understand that when you wind a clock, you build up tension in the spring, and that over time the tension is released into energy that drives the clock. And I understand that one of the fundamental pieces of a clock is responsible for controlling the orderly release of energy, so that the clock isn’t fast right after winding and slow hours later. How exactly does that piece of the device work?

What I would love is a book that starts with a very basic clock and works its way up. This would be the clockmaking equivalent of the Los Alamos Primer, say. (To make a very basic atomic bomb, take two subcritical masses of uranium and slap them together into one supercritical mass. To make a better atomic bomb, do rather more.) If this book I’m imagining took the technical apparatus and adjoined it to engrossing history and biography, it would start to look like the clockmaking equivalent of Richard Rhodes’s Making of the Atomic Bomb and Dark Sun — two of the three or four books that every human needs to read.

But that would be an altogether different book from Sobel’s, so I don’t fault her for this. If anything, her Longitude is an apéritif which wets the appetite for other, more technical books on timekeeping. Her bibliography, for instance, points to Landes’s Revolution in Time, which looks if nothing else like a great place to start.