Scientific tale of drama, intrigue

PUBLISHED : Saturday, 15 February, 1997, 12:00am
UPDATED : Saturday, 15 February, 1997, 12:00am

This is a little gem of a book that has become a surprise success, and deservedly so. It explains things that today we take for granted - such as how did longitude come about? Longitude may seem like dry lines on a globe, but knowing about it can be a matter of life and death.

On the night of October 22, 1707, Admiral Sir Clowdisley Shovell was at the head of five British ships heading home from engagements against the French in the Mediterranean.

A heavy fog made it difficult for the navigators to judge where they were and consequently four ships ran aground on the Scilly Isles. Two thousand lives were lost. This tragedy was directly caused by the inability of sailors to determine their longitude.

Dava Sobel has written with panache about the extraordinary man who eventually solved the problem of how to determine longitude, and the trouble he had winning recognition for his work. There is drama, intrigue, suspense, pathos and even humour in the telling.

Latitude lines are those that go round the Earth parallel with the equator. The zero-degree line of latitude - the equator - is not a line determined by politics but by geography.

In contrast, the lines of longitude all pass through both poles, and the prime meridian - the zero-degree longitude line - is arbitrary. At present it passes through London.

Latitude is easily determined by looking at the sun or a few stars, but longitude is far more difficult. To determine longitude at sea, one must know the time on board ship as well as that of the home port or any other known longitude. The time difference - if it is precise - will correspond to a geographical distance.

One degree of longitude is equal to four minutes of time all over the globe. But the best clocks in the 1700s lost a minute a day: they were completely useless over a 40-day voyage.

The greatest minds in Europe - Galileo, Newton, Halley and others - attempted to deal with the longitude problem.

In 1714 the British Parliament passed the Longitude Act and a fortune of GBP20,000 was offered to anyone who could solve the problem to within half a degree of a great circle.

The man who eventually won the prize showed in many ways the triumph of engineering over science.

John Harrison was a skilled, but rather stubborn carpenter with no special training in clock making. No one knows exactly why he began to make clocks, but he became one of the greatest in the craft.

Most clocks erred by 30 minutes a month. His, however, were out by only a second a month.

The wooden clock he built in Brocklesby Park in 1722, which took him five years to build, still ticks today.

Harrison's recognition was long in coming because of the animosity of astronomers - who felt their discipline should solve the problem - and also due to his own stubbornness and desire for perfection. But competition came from other directions, too.

There was one bizarre method for measuring longitude, for example, called the Wounded Dog. It was based on something called Powder of Sympathy. This powder, it was said, could cure a wound from a distance if applied to an article of clothing from the victim such as a bandage. Sprinkling the powder on the bandage would heal the wound.

It did not take long for someone to dream up the idea of purposely wounding a dog, putting it on a ship and then sprinkling the powder on an old bandage everyday at noon in London.

This would make the dog bark and the captain would then know the exact time in London and thus be able to calculate his position.

No one seemed too bothered about hurting the dog. It would presumably have to be hurt again and again so that the wound was not healed by the powder. Nor did anyone worry about the dog barking at other times.

When astronomers were not happy with a mechanical solution to the problem, the King had to come to Harrison's aid to ensure he won his prize and received the recognition he deserved.

Longitude by Dava Sobel Fourth Estate, $68