Such clocks did exist, but were unknown to the world outside the small Yorkshire village where John Harrison lived. Even the master clock at the Royal Observatory at Greenwich had to be adjusted almost every day, using solar and stellar observations.Īctually, the first sentence in the previous paragraph isn’t quite accurate. Yet early in the Eighteenth Century no clock existed which was accurate enough for this purpose, let alone capable of being rolled, tossed and exposed to extreme changes in temperature and humidity while remaining accurate. Being a minute off produces an error of one-fourth of a degree in longitude, which at the equator equals 17 miles. Accuracy and precision are both important. Finding longitude, however, requires comparing local time to the time at a standard meridian.

A fairly accurate estimate can even be made based on the length of the day (that is, the daylight period) versus the time of year. You can find latitude pretty simply it’s based on the height of the sun (or another celestial reference) above the horizon, which changes in regular fashion with the time of year and the distance from the equator. This book – and the A & E miniseries it inspired bearing the same name – made me realize just how important the problem of finding longitude was, and the difficulty of its solution. But he did so, and he did succeed, where all others had failed.īeing a student of the history of technological development I was already vaguely familiar with the problems of developing accurate timepieces, as well as the difficulty of producing a clock which was accurate and rugged enough to be used at sea to find longitude. In the process he had to abandon much of what he had already accomplished in order to succeed. For John Harrison’s greatest invention – something quite unlike anything he had built to that point – was made when he was in his seventies, and required him to take two long steps to one side… and move a century forward. It also disproves the conventional wisdom that creativity is an activity solely of the young.

The story of John (Longitude) Harrison disproves this. It has also been criticized as a romantic fantasy. The image of the lone genius, prevailing against the odds to make a better world, is an attractive one. Longitude book by Dava Sobel Reviewed by Rodford Edmiston Webmaster’s note : This is an old review from the previous version of the site, which we’re bringing in as a post so that it’ll be searchable in the reviews categories with newer content.

David sobel longitude