Harrowed Harrison’s long and lonely battle for longitude
I have consciously nurtured an indifference towards books with tantalising taglines. I always used to think (and still do) that they are nothing more than a flourish intended at catching a potential reader’s, or should I say a buyer’s, attention. It is one of the myriad developments resulting from growing consumerism and marketing gimmickry.
So I feel at odds when I concede that my curiosity towards this particular book was aroused considerably on account of the words printed on its cover – “the true story of a lone genius who solved the greatest scientific problem of his time”. I didn’t know how grave the problem was back in the eighteenth century and I wasn’t aware that the principal solution to the problem had been the undertaking of a single man.
Longitude is a brilliant book, more so because it literally raises a man from his grave and puts him back into the limelight that he thoroughly deserves.
John Harrison was born an ordinary man, but his continuous and devoted efforts over more than half a century grinding away, gnawing away at a problem that had been confounding the greatest minds of his time, finally led him to an elegant, artistic and beautiful solution. On the first page of the book, his five major clocks, labelled H-1 to H-5, are shown. That it took him nearly forty years to move from the first to the last shows the complexity of the problem he faced. But honestly, it is very difficult for the average person today to comprehend it. Even after having read this book, I am scarcely in a position to imagine the kind of travails this man went through.
In 1707, four British warships, destined for Portsmouth, ran aground off the Isles of Scilly due to their inability to calculate their position in the seas. More than fifteen hundred sailors perished. This disaster shook the nation to such an extent that the British Parliament passed the Longitude Act of 1714, according to which a prize of twenty thousand pounds was announced for a method to accurately calculate one’s position in the seas.
First let us understand what the actual problem was. When out in the sea, the problem wasn’t of determining the real local time. That could easily be determined by calculating the angular distance of the sun or the moon from the horizon, but this wasn’t a very accurate method – there were plenty of minor variations in the movements of the sun and the moon to sabotage such efforts. However, this was the best method they had back in the day so they settled for it.
So they have their local time. Now, one option was to determine the local time back home at that very instant. They could then convert that time difference into degrees, and the degrees into a distance in miles, determining their position.
Another option was to directly calculate their longitude. At that time, the foremost method of calculating one’s longitude was the exasperating lunar method. A table was made which recorded, for a given location, the angular distance of the moon with respect to the sun and a host of other heavenly bodies, at intervals of three hours.
So, for example, if the angular distance between the moon and a given heavenly body, as measured on a ship, turned out to have a value that, for the same two bodies, was listed, for the home port, at a time that was a certain number of hours ahead or behind, the difference could be used to calculate the present longitudinal position of the ship.
The real trouble was making those detailed tables which entailed thousands of observations over many years to account for those minor variations in the orbits of the heavenly bodies. Indeed, some of the greatest astronomers of the time, including Edmund Halley, spent years recording such information.
Even with the tables in front of them, there were long calculations and it used to take up to four hours to arrive at the answer – and that was if the weather was gracious enough to allow them to measure the angular values in the sky at all.
Harrison’s solution utilised the first approach – he had to develop a machine that could keep accurate time irrespective of the changes in temperature (which could lead to expansion or contraction of the pendulum in the usual clocks of the time), the wild rolling and pitching of the ship (which could ruin any internal mechanisms which the clock used to keep its time) and which was subject to least friction (to avoid dissipatory tendencies). So that, even months into a voyage, it was ticking as it would have if it had been kept at the home port, effectively telling the crew the local time back home at that very instant.
No wonder his first attempt, the H-1, weighed seventy five pounds. H-2 was even weightier, at eighty six pounds, and H-3 was sixty pounds. It was only with H-4 that he was able to reduce the size and weight considerably though.
The book also follows the opposition Harrison’s clocks faced from the believers of the lunar method. To them, and indeed most people at the time, it seemed to be a magical device which miraculously told them the local time at their home port. To this, they favoured the astronomical method which seemed to at least show them how they were arriving at the value. Indeed, as Sobel notes, had Harrison produced his masterpiece a century before he did, he could well have been accused of witchcraft. Such was the ingenuity of his device.
The precise knowledge of one’s position in the high seas is indispensable for navigation. One wrong calculation and the butterfly effect would take us into a completely different place, especially in the eighteenth century when voyages lasted for months at a time. In that context, the work Harrison did was not only commendable, but also required courage and commitment. This was the story of one man and his lifelong effort to solve the greatest scientific problem of his time.