|Home>Commentary>Perseverance & the search for longitude|
Perseverance & the search for longitude
My old printer failed last night in an attempt to print out my tax returns so I jumped in my truck and headed to Fry’s Electronics. I can’t go to Fry’s without being amazed. The store on Lawrence Expressway carries everything from refrigerators to chips (both potato and semiconductor).
When I walked into the store, I came upon an impulse-buy table that was stacked with Global Positioning System (GPS) receiver gadgets. Customers were looking over these hand-held navigation gadgets with great interest. I was interested too, but not by the affordable gadgets. Instead, my interest was peaked by a book I had just finished on the age-old search to figure out where we are. I wondered what the characters in this book would think about today’s technology.
Dava Sobel’s Longitude tells the story of one man’s search for a solution to what was considered the greatest scientific problem of his time. The man’s name was John Harrison. The problem was the calculation of longitude at sea. In solving this problem, John Harrison provides a wonderful example of the power of perseverance.
As we learned in our first geography class, latitude and longitude define your location on a map. Now, any experienced sailor can estimate latitude from the length of the day and the height of the sun and certain stars above the horizon. The laws of nature define the zero degree parallel of latitude at the equator. Longitude, as Sobel puts it, and here lies the problem, is defined by the whims of man.
Mapmakers have used lines of longitude and latitude since a few centuries before the birth of Christ. As noted, the parallels of latitude were fixed by nature. The zero meridian of longitude, being arbitrary, was up for grabs. Various governments picked there own politically correct zero meridians, usually near their capitals.
The English won the zero meridian contest by publishing the Nautical Almanac and Astronomical Ephemeris manual in such volume that it became the de facto standard for the world’s sailors. This popular manual, which was first printed in 1767, defined the zero (prime) meridian as running through Greenwich England. Once again, the pen won over the sword.
The calculation of longitude is quite easy and involves nothing more than basic arithmetic. Because the world revolves once every 24 hours, if you divide the 360 degrees of longitude by 24 hours, you get a value of 15 degrees equaling one hour of time. So, if you know the time-of-day where you are (determined from the sun) and the time-of-day at Greenwich England (from a clock), you simply calculate the difference in hours and multiply that by 15 degrees to calculate your longitude. The calculation is simple, the problem, in John Harrison’s 1700s, was difficult because clocks weren’t very accurate.
The calculation of latitude at sea became a national quest in England. The cry to find a solution was accelerated by various nautical disasters that were caused by errors in navigation. In 1707, twenty-one English ships returning from battle made a longitude error that resulted in the loss of four ships and 1,647 sailors. The people demanded action. Finally, the English Parliament passed the Longitude Act of 1714.
This act established a “king’s ransom” award of 20,000 pounds for a “Practicable and Useful” means of determining longitude. It also established a Board of Longitude to evaluate proposed solutions. Dava Sobel notes that this board might have been the first Research and Development agency. The 20,000 pound prize required an accuracy of ½ degree, which equates to an error of about 69 miles at the equator. There were lesser awards for less accuracy.
The search for longitude was divided into two camps. The scientific establishment long held that the answer lied in celestial observations and measurements. This big camp had all the big names, both living and dead, including Galileo, Newton, and Halley plus the political power of the Royal Observatory. The other camp had one lonely member, John Harrison, who believed he could construct an accurate clock.
In 1714, Harrison’s task was daunting. A successful clock had to operate in the harsh environment of sea travel, complete with violent motion, large temperature transitions, and high humidity. To achieve the required accuracy, a clock couldn’t accumulate an error greater than three seconds per day over the required six-week test voyage from England to the Caribbean.
Sir Isaac Newton, who was the chief scientist to the Board of Longitude, didn’t think such a device could be built. Others, including the Royal Astronomer, Nevil Maskelyne, wanted the celestial solution to prevail to the point where they deliberately placed numerous roadblocks in front of Harrison and his clocks. Sobel speculates that some of these roadblocks involved out-and-out skullduggery.
In a triumph of the individual over the establishment, John Harrison won the prize after a forty-year struggle. In the process, he built five incredible clocks. Each new clock improved on its predecessor in terms of ingenuity and size reduction. Importantly, in an eighty-one day round trip test from Portsmouth England to Port Royal in the Caribbean, and back, his fourth clock lost only five seconds.
John Harrison had the technical answer to determining longitude. There was only one remaining problem. Harrison’s clocks took years to produce and were very expensive. While the clock approach provided greater accuracy and ease-of-use to navigators, clocks had to be more affordable to replace sextants and lunar tables.
Two rivals, John Arnold and Thomas Earnshaw, solved this affordability problem and produced thousands of marine watches by refining Harrison’s design to allow mass production. The marine watch, which carries the formal name of chronometer, became the standard tool for navigation for years to come.
Meanwhile, back at Fry’s, we see the result of a similar process. The GPS system provided a beautiful solution to navigation when it went operational. However, the initial receivers were large and expensive. It was the quest for low cost, high volume semiconductors that opened the door to mass-market availability of these devices.
If the people who sought a solution to the longitude problem could comment on today’s GPS system, they would all find something to cheer about. Maskelyne would point to the use of celestial bodies (the satellites). Newton would find enough mathematics for a lifetime of research. John Harrison would just love the clocks.
(1) Sobel, Longitude, New Tork, Walker, 1995