The whys and wherefores of navigation Book Summary

Published in 1891, The Whys and Wherefores of Navigation by Rear Admiral Sir Frederick Evans is a fascinating glimpse into the world of 19th-century maritime navigation. It's a surprisingly accessible explanation of complex concepts, written for a general audience interested in how ships found their way across the oceans before the advent of modern technologies like GPS. While steeped in historical context, the book reveals fundamental principles that still resonate today.

This book isn't a 'how-to' manual for becoming a navigator. Instead, it's a detailed explanation of why navigational methods work. Evans meticulously breaks down the principles of dead reckoning, the use of chronometers for determining longitude, the intricacies of magnetic variation and deviation, and the application of celestial navigation using the sun, moon, and stars. He aims to demystify the science behind seafaring, making it understandable for anyone curious about the art and science of finding one's position on the globe.

One of the core lessons is the importance of accurate timekeeping for determining longitude. Before reliable chronometers, knowing your east-west position at sea was a major challenge. Evans explains how the Earth's rotation means that 15 degrees of longitude corresponds to a one-hour difference in time. A ship carrying a chronometer set to Greenwich Mean Time could compare the local time (determined by observing the sun) to the chronometer's time, and thus calculate its longitude. This was a revolutionary advancement, dramatically improving safety and efficiency in ocean travel. Imagine trying to navigate without knowing how far east or west you are – it’s like being lost in a maze with no sense of direction!

Another crucial concept is dead reckoning. This method, while seemingly basic, forms the foundation of navigation. It involves estimating a ship's position based on its last known position, its speed, the time traveled, and the direction steered. Evans stresses that dead reckoning is inherently prone to errors due to factors like currents, wind, and inaccuracies in speed estimation. However, it provides a continuous track and a framework for incorporating other navigational fixes. He uses vivid examples to illustrate how even small errors in estimating speed or direction can accumulate over time, leading to significant positional inaccuracies.

The book also delves into the complexities of magnetic variation and deviation. A compass points to magnetic north, which isn't the same as true north. Magnetic variation is the angle between magnetic north and true north at a given location, and it changes depending on where you are on Earth. Deviation, on the other hand, is the error caused by magnetic materials on the ship itself. Evans explains how navigators must carefully account for both variation and deviation to obtain an accurate compass heading. He details the use of isogonic lines (lines of equal magnetic variation) on charts to aid in this correction.

Finally, Evans provides a thorough explanation of celestial navigation, specifically using the sun and stars. He describes how to measure the angle between a celestial body (like the sun) and the horizon, known as the altitude. Using this altitude, along with the time of observation and tables of celestial positions (the nautical almanac), a navigator can calculate a 'line of position'. Where two or more lines of position intersect, the ship's position is determined. The book makes a surprisingly good attempt at explaining the trigonometry involved, even for readers without a strong mathematical background.

This book is perfect for you if:

• You're fascinated by the history of science and technology, particularly as it relates to seafaring.
• You want to understand the fundamental principles of navigation without getting bogged down in complex mathematical formulas.
• You enjoy reading detailed explanations of how things work, and appreciate a methodical approach to problem-solving.
• You're interested in the challenges faced by early explorers and the ingenuity they employed to overcome them.
• You have a general curiosity about the world and how people have historically oriented themselves within it.

Yes, absolutely. While GPS and electronic navigation systems are now commonplace, understanding the underlying principles of navigation remains vital. These systems can fail, and a solid grasp of traditional methods provides a crucial backup. Furthermore, the book fosters an appreciation for the skill and knowledge required of past navigators, and highlights the ingenuity of human problem-solving. The core concepts of dead reckoning, understanding magnetic fields, and using celestial bodies for positioning are still taught in navigation courses today, even if the tools have changed.

The next book to read would be 'Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time' by Dava Sobel. Evans' book explains how navigators used chronometers, but Sobel's book tells the compelling story of why they were needed and the decades-long struggle to create a reliable timekeeping device capable of determining longitude at sea. It provides the historical context and human drama that complements Evans' technical explanations beautifully.

The Whys and Wherefores of Navigation is a remarkable achievement – a clear, concise, and engaging explanation of a complex subject, written over a century ago. It's a testament to the power of fundamental principles and a fascinating window into a bygone era of seafaring. Despite its age, the book remains relevant and insightful, offering valuable lessons for anyone interested in the art and science of finding their way in the world.