Measuring Time: Challenging the Stars

Since Eratosthenes' age, humans know that we live on a sphere. In the 2nd century b.C., Greeks thought that it was only inhabitable a zone in the northern hemisphere, that nobody could live in the southern hemisphere, known by them as the "terra incognita", or "unknown land". In the 15th century, expeditions across the Globe proved that the South existed and that it was inhabitable as the North. The Earth was filled up with plenty of sailors who traveled from one place to another.

The seas, outside the Mediterranean, turned out to be immense. First, the Atlantic until arriving to the new continent. Secondly, the Pacific, which spreads towards the west and managed to circumvent the Earth, passing through Japan, the Philippines, and the entire Asian continent. Compared to these, the Indic Ocean looked like a small, "homely" sea.

The Astronomer by Johannes Vermeer, circa 1668




The navigation tools served to answer the following question: "Where are we?" Or as a better way to say it: "How could we get to a specific point of the geography?". The ability to be able to find it or not determined the subsistence of the boat or ship. Let's imagine in the 17th century a ship's crew in the middle of the Pacific who knew how to find an island where they could get some water and fresh food supplies, a crew who had in their navigation chart a highlighted place, which they were not able to find. What is more serious, think about a ship that approaches a coastline, the captain doesn't know how to determine exactly where is the boat or where is the coast; a storm, a strong wind could send the ship to the disaster, to crash against sea walls, or to a bunch of rocks, or to merely moving further from the coast, rather than approaching it.

What was needed to establish the position of the ship? Only two coordinates were needed, the latitude, in other words, the parallel where the boat was located, and the longitude, the meridian. People were able to determine the latitude in previous centuries to the 17th century, thanks to devices like the astrolabe, the sextants, or any other apparatus that could indicate the height of the sun or the stars during the night, having the Earth as a point of reference.

Let's take as real the movements of the skies (that is, let's think the Earth moves or, on the contrary, that the skies move). In any case, the truth is that we observe how the celestial sphere rotates 360 degrees (a complete rotation) every 24 hours, later every hour "revolves through 15 degrees", and so the distances between the meridians can be measured by degrees or by a time magnitude.

The longitude is associated with the Earth's movement, with time basically. Ptolemy knew this already but having as a reference point the spheres from the stars, which he considered that actually, were moving around the Earth. A meridian must be chosen and then, they have to measure the time from it. As one can see, the relation between longitude and time is not a contemporary discovery. What we do have now, that our ancestors didn't, is an agreement on which meridian is taken as a reference: in 1884, the International Meridian Conference agreed that the meridian of reference had to be the one that passes through Greenwich, a place near London (England), upstream the Thames, where a very prestigious astronomical observatory exists, which has been working since 1676.

Moving back to the problem of longitude, let's say that it could only be solved if there was a way to find out the distance between our location and the meridian of reference. The distance is measured in time and now a question arises: "what time is in the meridian of reference?". Imagine that it is known the exact hour of the place where we are, using time difference one could work out the "distance" from our point of location to that meridian of reference. For example, if at midday, we know that at that moment in the meridian of reference (let's say Greenwich meridian) the time is 4 pm, the distance would be 4 time zones, each one of 15º, so the longitude would be 60º west.

Until the 17th century, it was very clear that it existed 2 types of time, the one that was useful to organize everyday life, and the "true time", which was determined by the stars. The former one, regulated useful times for the most common human activities and it could be measured using water clocks, sand timers or mechanical clocks, and they controlled the differences, the time lapses. This time should be as similar to the solar time as possible, to the time measured by sundials. No one ever thought, however, that it could be found an accurate way to measure time before Galileo. Galileo Galilei described the pendulum laws. The pendulum clocks were able to measure time with extreme accuracy. Thanks to them, it could be established a convergence between the true time of the starts and the one from a human-designed apparatus. Despite this, however, this kind of clocks didn't solve the problem of longitude at the sea. To work well, they needed to be on very stable surfaces, and the ships at that time were very unstable. How one could build a clock that was able to resist against the sailing rigors?

It seemed an unsolvable problem in the early 18th century when the English admiralty organized a conquest where the winner would be the one who was able to find out a method to determine the longitude while at sea, allowing to have an error of less than 1 degree. The admiralty was worried about the continuous lost of ships, but the wreck on September 1707 of the entire crew of the navy at the proximities of the same British coasts, in the Isles of Scilly, was the catalyst for the Longitude Prize Convocation.

Prestigious scientists and sailors formed the "Longitude Board" in 1715 and this would prevail for more than 50 years. Everybody was waiting for the solution to be solved by astronomers, the most reputable scientists of the time. If it was possible to be able to know the hour in the reference meridian observing the stars from any given point on Earth, then people could define the time zones. The astronomers worked very hard in the 18th century and they finally managed to solve the problem in the last quarter of the century.

There was another solution to this problem though, a solution much more unlikely that didn't come from the astronomers, but from the clockmakers. These formed a guild where creativity to find new ideas was a mandatory skill, but on the opposite to astronomers,  they didn't have the trust from the Longitude Board to solve the problem that concerned them. The solution of the clock required designing a mechanism that wouldn't be affected by moisture or temperature, or by the movements of the boats while sailing, or by the storms, and that could be set on time just after leaving London, without going fast or delaying more than a second per day.

No-one would ever imagine that a machine like that could be designed, able to challenge the accuracy of the stars. No-one, except John Harrison, a clockmaker from London who turned out to be the most intelligent from all known artisans in history. Between 1730 and 1764, he manufactured 4 prototypes of watches that were surpassing all physical obstacles already mentioned. He used materials which reacted differently to humidity and temperature, invented a procedure to wind up the watch without having to stop it, he used materials that resisted abrasion and, especially, he reduced its size. From the first prototype, known as H1, which weighed more than 70 pounds, to the H4 prototype, which weighed just 3 pounds, Harrison managed to dodge all these obstacles as no-one else. In repeated demonstrations to the Longitude Board, he showed the successive prototypes that astonished the members due to their accuracy. But, they still have to be proven at sea. So, in 1764 when it was used the H4 prototype (the lightest one) to determine the longitude during an expedition from Portsmouth to Jamaica and the time deviations of Harrison's chronometer, which were inside the limits established in the Longitude Prize Convocation.

Harrison had just invented the "Marine Chronometer" with unprecedented accuracy, a mechanical watch that competed with the stars. As the inventor's stories don't always end up as well as in the books, he didn't have an easy recognition. The astronomers, on the other hand, had already managed to determine the longitude at sea by observing the movements of the Moon in the starred sky. One of the judges of the Longitude Prize was a director of the Royal Observatory, in Greenwich, named Maskelyne. It was reasonable that he preferred the astronomical procedures rather than the artisan ones, so Harrison had to dispute the Prize until the end, and he finally got recognition when George III became interested in his watches and chronometers.

At the end of the 18th century, sailors could eventually determine the latitude at sea, which meant an improvement in navigation safety.

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