I want to prelude my review by saying that this review is what I wrote for a book review assignment in my Maritime History class at UWF. I only got a 76% on the assignment, so don't attempt to copy/paste anything out - it won't do you a whole lot of good. Having said that, I do think what I wrote is likely good enough for a customer review on Amazon. :) Hopefully you find it helpful. The Illustrated Longitude by Dava Sorbel and William Andrews is a detailed book about the development of navigation through the discovery of calculating longitude. It was first published in 1998 by Walker Publishing Company, Inc, based in New York and sells for $32.95 in the United States. This book might be considered a second edition, even though it isn't labeled as such, because the first time it was published it apparently lacked the graphs, maps, charts, etc. that are found in abundance in this edition. Miss Sorbel and Mr. Andrews set out to describe to a presumably collegiate audience how the concept of longitude was developed and how one man, John Harrison, dared to defy the scientifically biased leaders and upper societal echelon of his day by developing a method of calculating longitude based on the mechanics of a watch rather than the passage of the night sky over the horizon. And that purpose is fulfilled in this 216-page text by colorful and captivating language, intriguing ideas, and a plethora of maps, charts, graphs, and pictures. Nearly every page has some sort of illustration on it, which enhances the reading and understanding of the point the authors are trying to make. The illustrations make it relatively easy to get into the mindset of the time. Miss Sorbel did include an appropriate amount of information for college-level study. She not only has good organizational skills, which she displayed by talking about subjects in chronological order as well as categorizing topics, but she did put that extra effort in to include as much detail about the history as she could. Her bibliography is as detailed as the text of the book itself and gives her work credibility. Looking at her bibliography, one can see that she uses contemporary sources as recent as 1996, as well as sources dating back to 1808. Using the newer sources shows that she is building upon the research and ideas of modern knowledge and thinkers; using the older sources gives her information, which is from a closer time period and mindset to when the events described actually took place, more authenticity. It is also refreshing to see her extensive use of maps, charts, graphs, etc. As was mentioned before, they are placed on nearly every page and they absolutely enhance the comprehensibility of the material. Without those images the things being described, whether they be maps or charts, astrolabes or compasses, time pieces or just a portrait of an individual being discussed would be nothing more than an abstract idea with nothing concrete to attach that idea to. Without a doubt, Dava Sorbel and William Andrews created a text worth reading. The Illustrated Longitude is full to the brim with interesting facts and an amazing history on a topic that many might not even realize is interesting until reading this book. But, with a colorful use of the English language, a detailed inclusion of historical data and a topic that inspires the imagination, this text is more than interesting. And, at only $32.95 it is less expensive, by as much as ten times, than the standard college text book.

This is a great read. The book is highly entertaining as well as being very informative. Dava Sobel makes a complex subject, the measurement of longitude, come alive. The story is not only that of a scientific and technical quest, but also of human conflict, told with great skill. It begins with the concept of longitude, why knowing ones longitude was critical and how it was treated prior to the seventeenth century. The key to longitude was time, or rather knowing the time of an event, at your location and at a reference location. The two primary methods to do this are via the use of a very accurate timepiece or through the use of a knowledge of the position of the moon relative to the sun and stars, both of which I discuss this in a bit more detail at the end of this review. The problem of an accurate longitude measurement was so critical that the British Government created a £20,000 prize for the solution to this problem. Most of this discussion is about John Harrison, a carpenter and self taught clockmaker, who developed a timepiece that was accurate enough to be used to measure longitude, and the British Royal Astronomers, primarily Nevil Maskelyne, who favored the method based on the position of the moon. The book discusses Harrison's creation of marine timepieces (chronometers) that were accurate enough to solve this problem and win him the prize, and the astronomers, primarily Maskelyne, who favored the moon position method and thus sought to discredit the clock approach and deny Harrison the prize. My only reservation about the book is that there is very little technical information about exactly how Harrison's chronometers operated. There is one figure showing an escapement mechanism and a very brief discussion of how he solved lubrication and temperature problems, but I did not feel that this was sufficient to really understand how his clocks worked. Thus, I feel that a serious student of clocks would likely to be disappointed in the technical aspects of the book. However, a more general reader like myself could overlook this deficiency and focus of the human aspects of the book. I was able to find enough technical information about the operation of watches from the Internet to satisfy my needs, so the lack of this level of detail did not cause me to downrate the book from 5-stars. THE MEASUREMENT OF LONGITUDE - The simplest event to use to determine longitude is high noon, the time when you sun reached its highest point in the sky. If you had a watch set to 12noon at a reference location you could know your longitude based on the time, on this watch, that you locally observed high noon. For instance, if this watch was set so that it registered noon at Greenwich England (the location of the Royal Observatory), and you saw the sun reach it highest point at 1 o'clock, then you knew that you were one hour west of Greenwich. Since a day (one complete earth rotation) is divided into 24 hours and a circle is divided into 360 degrees, each hour of difference corresponds to 360/24 or 15 degrees of longitude, or about 1000 miles at the equator. Unfortunately, in the early 18th century there was no clock that could operate on a ship that was accurate enough to yield time measurements that could be used to accurately perform this task. If the clock ran to fast or too slow, say by only one minute per day, then in 10 days it would be off by 10 minutes or 1/6 of an hour or 2.5 degrees of longitude. At the equator this corresponds to about 1000/6 or 166.7 miles, which was clearly unacceptable. Even a much more accurate clock, say one that was off by only 10 seconds per day, would be unacceptable for a long voyage. Such a clock would be off by 300 seconds in 30 days or 5 minutes, yielding an error of 1.25 degrees, or about 83 miles at the equator. In practice, two chronometers are used, one set to the reference time and one continually adjusted to 12 O'clock at local high noon. Since the local clock was continually being adjusted it did not have to be as accurate as the reference clock that was not adjusted. Using a locally adjusted clock allowed one to determine the longitude at any time of day, instead of just at high noon. Another approach was to chart the position of the moon relative to specific stars, or the sun. One could then determine the longitude by using an almanac showing the time at Greenwich when the moon was in a particular position and when it occurred locally. The local time was determined by observing high noon. This method also had limitations as it required many laborious calculations, which were subject to error, and it could not be used when the moon could not be observed. A still earlier method used the eclipse of the moons of Jupiter as the reference, but this required a very accurate telescopic measurement that was very difficult to do on a swaying ship.