Introduction
Engineering — the sole pursuit of many an MIT student — is a great deal more than just solving engineering problems. It lies at the quarrelsome intersection of theory and practice, butting up against social boundaries and the need for new ingenuity, with problems arising from take, but shaping the future, where it needs to draw on human capital for a mechanical result. The Longitude week is a case study in engineering, centered on the work of John Harrison, inventor of the marine chronometer. His story exemplifies both in its heights of innovation to solve a problem then simultaneously at the edge of science and needing the finest points of craft, and every aspect of the difficulties that come with it.
Readings
| SES # | TOPICS | READINGS | QUESTIONS |
|---|---|---|---|
| 11 | Harrison and the longitude problem |
Laycock, W. S. "John Harrison, The Man Who Mastered The Pendulum." Horological Journal (February 1976): 5-13. Bruton, Eric. "The Time at Sea." Chapter V in The History of Clocks and Watches. New York, NY: Crescent Books, 1989, pp. 85-105. ISBN: 9780517689097. | (PDF) |
| 12 | Clock design issues and engineering |
These articles describe details of Harrison's inventions for time compensation, the grasshopper escapement, and some aspects of H4. They are useful for truly wrapping one's head around the engineering, for which additional time might be spent in class. Laycock, W. S. "Time Compensation." Chapter VIII in The Lost Science of John "Longitude" Harrison. Ashford, England: Brant Wright, 1976, pp. 63-70. ISBN: 9780903512077. Hastings, Peter. "A Look at the Grasshopper Escapement." Horological Journal (August 1993): 48-53. Gould, Rupert T. The Marine Chronometer: Its History and Development. Woodbridge, England: Antique Collectors' Club, 1988, pp. 70-78. ISBN: 9780907462057. |
Labs
Three possible labs for this module are described briefly below. In the seminar, we typically did the "take apart and put together" lab.
Observe a Clock over Time and Conditions
We supply the students with mechanical, wind-up desk clocks. The task: for one week, record the time of the clock, relative to an electronic clock. Try to detect (a) the drift of the clock, (b) the effect of temperature, and (c) the effect of winding the clock. Students may construct their own experiments for (b) and (c), which might consist of recording drift over the day versus the night time, and measuring time loss with different winding strategies.
Take Apart a Clock and Put it Back Together
The clocks we use (mechanical, wind-up desk clocks) have a large plastic casing (a face about 5 inches diameter and a body 2 inches thick), making them ideal for taking apart. The first step is to unwind the clock entirely. The power spring can be dangerous when it is let loose. Then, as the students take the clock apart, they must keep track of the pieces and how they fit together. Identify the power, the timing element, the escapement, the remontoire, and the gear logic to turn the various hands. Draw a flow diagram of how the clock works. Then put it back together.
Construct a Clock and an Escapement
A clock needs a power source, a timing element, and something to moderate between them (the escapement), but an unlimited number of materials and configurations will work. Students may work in wood, water, or anything else they can find (though electronics are discouraged). The best clocks we have seen have consisted of wood and string. Draw the design beforehand and predict how long it will run, how quickly, and how evenly. See how well the constructed object fits those predictions.