Greenwich means time

Martin Rowe- September 5, 2012

I recently spent a week on London with my family. On August 25, we boarded a boat ride down the River Thames to Greenwich, home of the Royal Observatory. The Royal Observatory is where that imaginary, arbitrary line, the Prime Meridian, passes through, separating the Eastern and Western Hemispheres.

Just before the trip, I started reading The Illustrated Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time by Dava Sobel and [illustrated by] William J.H. Andrewes from the public library. The book tells the story of John Harrison, who determined that if you know the time difference between your location and a reference location, you could calculate your longitude.

The photo below shows me standing in Greenwich, the Prime Meridian is below me and the rain is above. In addition to being the home of the Prime Meridian, Greenwich is also home to GMT, Greenwich Mean Time, the world standard for timekeeping.


I'm standing on the Prime Meridian after a long walk in the pouring rain.

The museum in the Royal observatory contains the four time pieces that Harrison built, each one improving on the other. The time pieces, called H-1 (1735), H-2 (1737), H-3 (1756), an H-4 (1759) still work today, a testimony to Harrison’s genius and skill. The video below the photo shows Harrison’s H-1 still works--unbelievable.


John Harrison's first time piece in his quest to solve the longitude problem by measuring time


Click on the video to see Harrison's H-1 still operating

In building his time pieces, which displayed the time as a reference location—a ship’s hop port—Harrison had to overcome numerous technological and scientific problems. Changes in temperature, humidity, and the Earth’s magnetic field all contribute to a timepieces inaccuracy, as will vibration. Harrison had to design his clocks to overcome all of these problems. Thus, he had to understand mechanics, temperature expansion and contraction, materials, and a host of other disciplines. He also had to overcome the problem of keeping the time piece running during winding.

Harrison’s H-2 overcame problems with H-1 such as its ability to withstand temperature changes. The photos below show the H-2 and a close-up of the plate indicating that Harrison built H-2 for King George II.


Harrison's second time piece, H-2, an improvement on its predecessor.


In the H-2, Harrison included a plate saying that the time piece was for King George II.

Harrison’s H-3 contains 753 individual parts. The fact that he was able to not only conceive of this, but build it to tolerances that would make it work is miraculous to me. Clearly, Harrison was a master machinist. He had to design and build all those parts to exact specifications. Clearly, tolerances in the parts would affect the clock’s accuracy.


The H-3, a further improvement, has 753 parts. The video below shows that it still keeps time.



Harrison’s H-4 was more like a pocket watch that its clock-looking-predecessors. That’s because it was based on a pocket watch made by John Jefferys and given to Harrison in 1753 even though, according to Sobel, it “has Harrison’s name all over it, metaphorically speaking.” Jefferys based his design on Harrison’s H-1, H2, and H3. Harrison then worked with Jeffery’s design to develop H-4, which proved its value on the high seas. H-4 won Harrison a prize of £20,000 from the British Government through the Longitude act of 1714.


The H-4 proved that Harrison solved the longitude problem by keep ting time accurately enough for navigators to know their longitude and avoid shipwrecks.

Inventions such as Harrison’s are, to me, more impressive than any GPS or cell phone we have today. Harrison and his contemporaries were true engineering and scientific pioneers. Harrison was a mechanical hero, akin to the Electrical Heroes of his time.

I’m still reading Sobel’s book.