Dava Sobel's description of the search for an accurate means to measure longitude was a surprise best seller when first published. This latest, celebratory edition is prefaced by an introduction by Neil Armstrong. Does it add to the package?

Sobel took what was once an intractable problem - finding a means to work out precisely where you are - and turned it into a very readable account, making the history and science readily accessible to a popular readership. Working out latitude is not particularly difficult - the equator is a fixed point and observation of sun, stars, and length of day make it relatively easy to determine how far north or south you are.

But longitude? Because the earth spins (more or less) on a north/south axis, the two poles act as fixed points in space. There are no such fixed points on the equator - every point on the equator undergoes a complete revolution every twenty four hours. Longitude has always been problematic, and for the seafarer, that problem could easily prove fatal.

The solution came in the creation of clocks which would keep good enough time at sea, and the man responsible for their invention, Harrison, emerges from Sobel's book as a determined, driven man.

It's a fascinating little book, written in a highly accessible style. It's quite a quick read. It's a highly enjoyable read. It's also a stimulating read, and must have encouraged a few people to delve further into history and science.

But does it deserve a new edition? Well, the cachet of Armstrong's introduction is a reminder that long distance sea travel was once as dangerous as current space travel. It's unnecessary. Sobel's story is exciting enough, and will absorb you with or without an introduction. It remains an excellent little volume and a worthy publishing success - maybe it's time you read it again!