Longitude by Dava Sobel (Book Review)

Informed and scientifically minded persons are generally aware that John Harrison was a man who solved the longitude problem by the use of very precise clocks in the 18th century. My first exposure to his story came from the 3-part series produced by the BBC,[1] with Harrison played by the very capable Michael Gambon.[2] Dava Sobel’s short and sweet book Longitude, coming in at a crisp 175 pages, transports the reader to the perils of international navigation that plagued explorers, merchants, and the general commerce of European empires in absence of a measure of longitude before the late 18th century. Sobel’s book provides us with a gripping account of the stubborn and persistent Englishman who never lost faith in the ability of his mechanical device to solve the longitude problem. After finishing Longitude, one is struck again by the extreme contingency of our luck in receiving Harrison into this world at the time and place and manner in which we did. A small deviation in the circumstances of the world would have meant many more years of costly ignorance dearly payed for by the lives of sailors.

As every schoolchild knows, the world is divided into theoretical bands of latitude and longitude, the former measuring the relative distance from the equator, and the latter representing measurements of distance between east and west.[3] Dava reminds us while degrees of latitude are a scientifically determined measurement,[4] one’s absolute position longitude is not (longitude to whither?). This interesting theoretical distinction has important physical characteristics in that one cannot use the visual cues associated with latitude for longitude. The clues of latitude lie in the heavens. At any given day of the year, on a given point of longitude, it is easy to appreciate that the sun will rise and set at a different time depending on one’s latitude. In other words, in my home city of Vancouver, the sun will set much faster than in San Francisco, even though both cities lie on the roughly the same longitude. Thus using the durations of sunlight would give one way of determining latitude. However, despite the fact that sun rises earlier in say Winnipeg than Vancouver, given these two cities are roughly on the same line of latitude, there is no clear sign of longitude as the duration of the day is roughly equal for both cities as they are on similar latitudinal lines. In an age before telecommunications, one could not simply ring up London and ask how many hours ago the sun rose.

Instead, Harrison knew that if one could bring a clock which was set to the port of departure’s local time, and one knew the time where one was (by say seeing when the sun rose) it would be easy to determine how far east or west you were of your original spot. Ah yes, there’s the rub. For before Harrison, getting a clock to keep time in a sedentary, well-ventilated and climate controlled setting was very challenging. Consider a clock that runs either one-minute too fast or slow. There are 360 degrees of longitude which span all twenty-four hours of a day, or 4 minutes per degree. If a ship needed two weeks to cross from London to New York, for example, then by the end of the voyage, the 1-minute-too-fast (or slow) clock will provide a 14 minute error, translating into 3.5 degrees of longitude or about say 200 km off: a significant error indeed.[5]

And by the start of the 18th century these errors were becoming national catastrophes. In 1707 a haughtily sounding Admiral Clowdisley Shovell was leading his fleet of five ships back to England. The ships were within a day’s sailing of Land’s End, but their position of longitude was misjudged and instead of finding themselves close to shores of Brittany, they were heading straight towards the Scilly Islands, rocky outcrops that would smash any ship to pieces that made contact with them. The “dirty weather” that morning, as the Admiral put it, obfuscated the disaster looming. Within short order four of the five ships struck the rocks and were sunk. Only two crewmen washed ashore, including Clowdisley, although he died shortly after.[6]

The problem of not being able determine if one was at the Île d’Ouessant or the Scilly islands was becoming increasingly grating. The great mathematicians of the age had solved the fundamental laws of gravity and motions of celestial bodies, Britain had established an empire on whose landmass the sun never set, and international companies were setting up branch offices in Bombay. The pomp of power (and commercial interests) demanded a solution finally be put forth, and in 1714, the British Parliament passed the Longitude Act and delegated the responsibility of evaluating proposals to the Board of Longitude. The Board was indisputably a blue ribbon panel with its membership composed of the Astronomer Royal, the President of the Royal Society, the first Lord of the Admiralty, the speaker of the House of Commons, the first commissioner of the Navy, and the Savilian, Lucasion, and Plumian professors of mathematics from Cambridge and Oxford.[7]

And yet any betting man of the time, would have surely placed his wager of the astronomers and their ilk in solving the longitude problem. Surely the clock-work universe and its unerring celestial patterns held the answers of so trivial a geographic conundrum? This is certainly what the intellectual elite assumed. In principal, a solution no doubt could be garnered from the heavens. After all, once their movements were known, the stars and the moons had a predictable pattern that varied depending on where one was on the globe. And yet, like solar energy today, unless it is easy to use and reliable, expecting market adoption was far-fetched. Sobel highlights that even the most sophisticated astronomers had trouble implementing the ‘lunar distance method’.

It was in this context that Harrison was born in Yorkshire in 1693. His father was a carpenter and custodian on a rich landowner’s estate, which at least provided the opportunity of Harrison to escape the most extreme deprivations of poverty. The rest was pure bootstraps. An itinerant clergyman provided Harrison with some treatises on natural philosophy which was the first proper fuel that the voracious and intrepid John experienced as a teenager. By the age of 20 Harrison was building his first pendulum clocks. No doubt the extreme intricacy and physical complexity of a timepiece’s internal organs drew John in. Being near to the city of Hull it was likely that John had heard about the Longitude prize from the locals whose community was intimately related to commerce and maritime travel, being the third largest port in Britain at the time.

When Harrison arrived in London in 1730 to propose his mechanical solution to the longitude problem, he sought out the advice of the current astronomer royal, Edmond Haley, who had succeeded John Flamsteed. Luckily for John, Haley was an amical and good-natured man.[[8]] While Haley was obviously in the astronomical camp, he was a true scientist in that he wanted all ideas tested with equal vigour and sent John to George Graham, one of London’s best clock makers, to get his opinion on Harrison’s first timepiece (the H-1). Despite initial frictions, Graham became convinced of John’s designs and lent him political as well as pecuniary support. After convincing the Board to meet to hear his idea, Harrison also convinced them of the need for an improved prototype before it was tested. Many years and several stipends later, Harrison’s son William took the H-4 on the HMS Deptford to Jamaica. The device had a chance to prove its worth in several days by helping the captain determine how close they were to the Madeira islands and ensure the men could get their necessary liquids of inebriation (the beer had been thrown overboard several days earlier due to spoiling). Captain Digges was instantly won over by the device.

By the time the device had reached Jamaica, it had lost only seconds of time, and should have been the winner of the Longitude Prize at that very moment. However, Harrison and his son would be stymied for years to come by the villainous Nevil Maskelyne and James Bradley, both of whom were the astronomers royals succeeding Haley. To appreciate the injustice these two men inflicted on Harrison one must read the book. However, in addition to the satisfying conclusion of John eventually receiving his rightful due (helped in fact by King George III), the story serves as an important reminder in our contemporary age of the difference between science and scientists. The former is a method of discovering truth, the latter are the purported users of the former approach. However, all human-incarnate forms are inevitably fallen.

I cannot praise this book too highly. Firstly, its brevity is astounding given how much the reader feels she has taken away from the work. At no point do we feel Dava shortchanges us on the facts or details. On reflection, the author is able to be so contrite as she does not waste space with pop psychology. The reader is given the opportunity to judge the characters of the people we meet in this historic period by the facts and context we are provided. The result is that the reader comes away with an almost more intimate Harrison than we could have expected with longer biographical detailing. An additional feature this book has is the incredibly apt quotes and poems adorning the chapter titles. I have included my favourites at the end of the article. Overall, this book provides a very well written example of the power of the science and engineering to solve important human challenges. It also shows the problems that result from the interaction of science and human institutions. We must always remember that the scientific community or scientific bodies do not always have the best interests of science at heart any more than an industry group has the best interest of the ‘economy’ at heart.

Selected Poems from Longitude

My Father’s Watch, John Ciardi

One night I dreamed I was locked in my Father’s watch

With Ptolemy and twenty-one ruby starts

Mounted on spheres and the Primum Mobile

Coiled and gleaming to the end of space

And the notched spheres eating each other’s rinds

To the last toth of time, and the case closed.

Don Juan, Lord Byron

Oh! She was perfect, past all parallel--

Of any modern female saint’s comparison,

So far above the cunning powers of hell,

Her guardian angel had given up his garrison;

Even her minutest motions went as well

As those of the best time-piece made by Harrison.

Richard II, Shakespeare

How sour sweet music is

When time is broke and no proportion kept?

So is it in the music of men’s lives.

I wasted time, and now doth time waste me;

For now hath time made me his numbering clock;

My thoughts are minutes.


  1. From the three volume novel, to Satie’s Gnossienne’s or even the Triumvirate, there is a there is something about this first prime number inspires utter confidence. 

  2. Sir Michael Gambon is well known to us now as the ‘new’ Dumbledore. 

  3. An easy mnemonic I have employed to remember the difference between latitude and longitude is that the former sounds like ‘altitude’ which tells you how ‘high’ you are from the equator. 

  4. In the sense that once you accept that there is a magnetic pole and its reciprocal, the band that runs exactly equidistant between the two poles is the equator, and the relative distance between the equator and a given pole can be divided into units, which we use degrees of latitude to measure. 

  5. The earth’s circumference is 40,000km, meaning that there are 111km per degree at the equator. Hence 3.5 degrees translates into 389km, at the equator, and I ‘guestimated’ about 200km for a higher latitude. 

  6. While not in any way relevant to the story of longitude, the drama surrounding that the event and Clowdisley are fascinating. First, that morning Clowdisley had a sailor hung for daring to question their position of longitude. How sweet it would have been for executed sailor to give Cowdungsly a look as their ships sunk to the ocean. Second, when against all odds Clowperton was one of the two souls that washed ashore alive, a local woman murdered him to steal his jewellery! She later confessed this to a country parson on her death bed and provided his family ring as proof of her crime. What a lesson; I hope Shovell profited from it! 

  7. An unrelated side note: despite Cambridge currently being the most successful of the Oxbridge duo, the latter of the pair indisputably holds the balance of Prime Ministerships in the 20th century. 

Written on May 18, 2016