Steve Van Slyke's Reviews > Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time

Longitude by Dava Sobel
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Jan 28, 2011

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bookshelves: history, science, kindle
Recommended to Steve by: Science & Inquiry Group
Recommended for: Those who want an overview, but not the details
Read from January 24 to 28, 2011

If allowed I would have given this book 3.5 stars. I enjoyed the history, which is well told. What I missed were illustrations and some explanation of the basic mathematics involved. For example, nowhere in the book does the author explain how an accurate timepiece resulted in the determination of longitude at sea beyond the idea that the Earth rotates 15 degrees on it axis in one hour and if one knows what time it is Greenwich, longitude can be determined. Perhaps this could have been explained in an appendix so as not to bog down the narrative flow. She did not explain that the navigator first has to determine the time of local apparent noon using a sextant or equivalent, and then use that time adjusted by a factor called the equation of time in order to convert the time difference between apparent noon at Greenwich and apparent noon at the ship into degrees and minutes of arc; i.e., longitude.

As for illustrations or photos I would loved to have seen what some of the clocks looked like as well as their components, e.g. the grass hopper escapement.

The author makes one mistake of terminology when referring to the problems of errors in magnetic compasses. She calls the errors variation, when in fact such errors are referred to as deviation. She correctly and previously defines variation as the differences between magnetic north and true north which vary geographically. So in order for navigators to convert magnetic bearings to true bearings they have to apply corrections for both variation and deviation. To help remember whether or add or subtract westerly or easterly errors, navigators use the mnemonic aid "Can Dead Men Vote Twice At Elections" (Compass->Deviation->Magnetic->Variation->True Add East). For the reverse it is Timid Virgins Make Dull Companions At Weddings.

The Quest for Longitude: The Proceedings of the Longitude Symposium Harvard University, Cambridge, Massachusetts November 4-6, 1993 is recommended for those who enjoyed Sobel's book but want more background.
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Steve Van Slyke Just started reading the Kindle edition. Disappointed to discover that it does not contain the foreword by Neil Armstrong alluded to on the cover.


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