Subscribe
Subscribe
MY AMERICAN SCIENTIST
LOG IN! REGISTER!
SEARCH
 
Logo IMG
HOME > PAST ISSUE > Article Detail

MARGINALIA

Finding Out the Longitude

J. Donald Fernie

The Board of Longitude

Even decades after the founding of the royal observatories, the astronomers were not making much progress on the longitude problem, and meanwhile lives and valuable cargoes continued to be lost to shipwreck. Several maritime nations offered considerable rewards to anyone who could solve the problem adequately. In 1714 Britain offered a prize of £20,000 to anyone who could convince a panel of experts, known as the Board of Longitude, of a method that would determine longitude to within half a degree after a trans-Atlantic voyage. A sum of that magnitude, worth millions of dollars in today's terms, was, of course, a clarion call to every crackpot everywhere.

Very soon the Board of Longitude needed a secretary to hand out stereotypical answers to stereotypical proposals. Some applicants simply had no idea what the longitude problem was about. Thus Dr. Woeman wrote, "acquainting the Board that he can express p and the ratio of 1 to -2 in integrals, and that this comprehends the discovery of the Longitude." Others had some inkling of the problem but proposed hopelessly naive solutions. Mr. Owen Straton, for instance, had to be informed that a sundial would not win the prize. Only slightly better on the scale of naivete was Mr. Haldanby's offering, which noted that sailing northwest near the equator meant that having increased your latitude by 1 degree, you had also moved 1 degree westward in longitude, and that he could provide a table that would apply to other latitudes and directions. The difficulties introduced by ocean currents seem not to have occurred to him.

Figure 2. Using the angles between the moon and various stars . . .Click to Enlarge Image

A proposal that received a good deal of attention beyond the Board was that of Whiston and Ditton. William Whiston had succeeded Isaac Newton as Lucasian Professor at the University of Cambridge, and so his opinions on scientific matters carried some weight. The Whiston-Ditton scheme envisioned small ships being anchored at intervals of a few hundred miles across an ocean, it being "known" that the North Atlantic was nowhere more than 300 fathoms deep. Each ship would have a powerful gun that would fire a shell 6,440 feet vertically upward at midnight each night. At the apex of its ascent, the shell would explode with a brilliant flash and monstrous boom that could be seen and later heard as much as a hundred miles away. This would allow other ships to locate themselves relative to the anchored ship, whose longitude would have been established by, say, lunar eclipses. Problems of staffing and provisioning such ships, keeping enemy ships and pirates at bay, and so forth, were waved away. A competitor noted that this proposal was "a very whimsical Notion, looking very Ridiculous in Mr Ditton and Mr Whiston; the first of which Gentlemen I do not know, but as for the other, People says he is a little beside himself, or rather, if he has any such Thing as Brains, they are really crackt."

But the pièce de résistance of all such schemes was the one based on "the powder of sympathy." Its author was anonymous and very likely wrote satirically (since anonymous inventors are not usually awarded major prizes). The method hinged on a medicinal powder that when applied to a wound would cause the wounded person to start up, possibly with a cry. Nothing unusual there, but the author claimed to have found that if the powder was applied not to the wound itself but to a bandage that had previously been on the wound, the effect was the same. Thus it was proposed that each ship carry a wounded dog, and that a bandage from the wound be left at Greenwich, where at precisely noon each day it would be dipped into a solution of the powder of sympathy. The dog, wherever in the world its ship was at that moment, would then obligingly yelp and the mariner could then note the local time and so find his longitude.

As the years went by, the preferred methods of finding longitude narrowed to two: improvements to the method of lunar distances and improvements in the marine chronometer. Lunar distances continued in use well into the 19th century, but in the end it was the chronometer that won out, and in our own time, of course, radio signals and now the Global Positioning System have reduced the problem to triviality.

© J. Donald Fernie








comments powered by Disqus
 

EMAIL TO A FRIEND :

Subscribe to American Scientist