The yelp of an old sea dog

THE DIGBY'S came to prominence in the 16th century when one of their number married the heiress of the Earl of Kildare, thereby…

THE DIGBY'S came to prominence in the 16th century when one of their number married the heiress of the Earl of Kildare, thereby acquiring extensive lands in Geashill, Co Offaly, and becoming "a person of importance in King's County, Ireland's. Some generations later, a scion of the family, one Sir Kenelm Digby, made his name in quite a different way.

As a Roman Catholic, Sir Kenelm was regarded with suspicion by Cromwellians. He thought it wise to absent himself for a while in France, and when he returned after the Restoration, he announced that he had discovered a remarkable panacea - a powder that could heal a wound at any distance. All one had to do was to apply the powder to some artefact that had come into contact with the ailment. The only disadvantage was the cure could hurt patients allegedly would jump in pain when some distant item recently in contact with their sore was sprinkled with a dash of Digby's powder.

All this comes to mind because a week or two ago, a lady on the letters page took Weather Eye to task, and rightly so, for gender bending the author of a book called Longitude. The book, still hovering near the top of the bestseller list in Britain, was written, of course, by Dava Sobel, not David, and it tells the story of the search over many centuries for a method to determine longitude at sea.

In principle it could be found by comparing the time at the location of the ship with the time at Greenwich, since each hour of time difference would account for a 15 degree shift in longitude. Local time could be determined from the sun at noon, so all that was needed was a clock that kept accurately to Greenwich time, but in practice late 17th century timepieces were unequal to this job. Sobel tells us of other methods that were tried, undoubtedly the most bizarre of which was the yelping of a wounded dog.

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Before a transatlantic voyage was embarked on, a wounded dog was put aboard the ship, care being taken to leave in the custody of some trusted person ashore a bandage that had touched the canine sore. The assistant's job was to apply some of Digby's powder to the bandage at noon precisely every day in Greenwich. Naturally, the unfortunate mid Atlantic dog would yelp in response to this distant painful stimulus, thereby providing the navigator with an accurate time signal. By comparing this to the ship's clock, which was reset regularly to local time, the longitude of the vessel could be quickly calculated - or so, at the time, it was apparently believed.