Thursday, March 06, 2014

A thought on the development of means to measure longitude.

I have been reading Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time by Dava Sobel. This is a fun read. It focuses on John Harrison as a lone genius who (with helpers) in the 18th century created a solution to the technical problem of accurate time keeping at sea (in the small, unstable ships of the time). I first read and commented on the book in 2003. I recently saw and commented on the film made based on the book.

It occurs to me that there is a deeper story.

Part of that story is the development of long voyages from 1500 on from ports in Britain, France, Netherlands, Spain and Portugal. This was the time when those countries developed global networks of colonies. There was a huge and profitable trade from Asia, and a trilateral trade in the Atlantic -- slaves, sugar, and rum, not to mention the gold and silver. These nations developed navies to protect their shipping, to attack the shipping of other nations, and to conduct war. As Dava Sobel points out, the cost of the inability to accurately determine latitude included an increasing number of ships lost and deaths at sea. It also included huge financial losses. No wonder that these governments offered incentives to develop a means for measuring longitude -- a means I suspect that they would all intend to keep as state secrets.

My mother was from England and I suppose that I am more aware than of English class consciousness than most of my fellow Yanks. The importance of class would have been much greater in 18th century England that it is today. John Harrison was originally a carpenter, someone who worked with his hands. The astronomers of his time would have been gentlemen who had attended universities. There would have been a huge class difference. Indeed, the ships officers in the British navy would have been gentlemen, while the navigators (who supported Harrison) may well have been from the working class. The importance of King George III intervening on the part of the Harrisons, requesting that the Prime Minister see justice done for them, would have been huge in status conscious England.

Astronomy, from about 1650 to about 1750, was probably the highest prestige area of science or natural philosophy. There was a chain of astronomers from Copernicus (1473-1543) to Tycho Brahe (1546-1601) to Kepler (1571-1630) to Galileo (1564-1642) to Christiaan Huygens (1629-1695) to Isaac Newton (1642-1727) to Edmund Halley (1656-1742) who each contributed greatly to the understanding of astronomical observations. Galileo and Huygens made important contributions to the understanding of the pendulum, and thus to the technology of pendulum clocks. Technology advanced with the development of telescopes, sextants and other instruments. Newton, with the theory of gravity developed a theory that with his invention of calculus allowed for calculation of orbits. His work in the study of light and optics led to the invention of the reflecting telescope. Rene Descartes (1596-1650) and Leonhard Euler (1707-1783) developed mathematical techniques used by Newton and other astronomers. The Gregorian Calendar was introduced in 1582, based on the recognition that the Julian Calendar had an inaccurate measure of the length of the year, based on the work of the Church's observatory, and that a new calendar was needed to restore important religious events to their intended place in the seasons.

I suppose that physics in the 20th century was comparable in the prestige of physicists, the flow of new science from their work, and the public appreciation that their findings created. The thought is supported by the fact that Newton and Halley were sequentially the presidents of the Royal Academy.

As physics in the 20th century led to new technologies, so did astronomy in the 18th. Astronomers developed means of measuring time by observing astronomical events such as the occlusions of the moons of Jupiter, and tables that would allow determination of exact Greenwich time from that observation. Comparing Greenwich and local time allowed calculation of the local longitude. While the method was of limited practicality at sea, it was used in terrestrial surveying. Indeed, determination of longitude by lunar observation at sea existed in parallel with the use of marine chronometers for many decades.

Ultimately the development of the marine chronometer solved the problem of measuring longitude at sea. As expected, it was not the pendulum clock developed in the 17th century that sufficed as it was too sensitive to ships' motion and temperature change.

I accept Sobel's analysis (and apparently the judgement of the Parliament) that Harrison deserved the prize. Still, there was a great body of mechanical technology developed in the 18th century that must have contributed to his invention, and perhaps equally important to the ability to manufacture hundreds of chronometers based on his designs. Of course, as Sobel notes, there were watch makers who had their own techniques and who helped Harrison; pocket watches had been available from the 17th century. But this was also the time when the mechanical means of manufacturing cotton cloth were being developed, as were steam engines and the machine tools for their production. I can only suppose that the people who developed the commercial marine chronometers based on Harrison/s ideas, did so using techniques that had been developed by others, much as Harrison himself used scientific knowledge developed by the natural philosophers working on mechanics. (Sobel discusses the development of manufacture of marine chronometers by commercial watchmakers in her penultimate chapter.)

Thus there was an important and growing humanitarian and economic need for a technology, a scientific basis for development of that technology, a body of related technologies that could be applied in developing a prototype and then a commercial product with its manufacturing processes, and finally a man of inventive genius, passion for the task, and almost inhuman persistence.

A Harrison type Chronometer from after 1800.

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