The Great Longitude Mystery

D Vautier
5/2019

When I was 12 years old I built my first sextant.  The base was plywood in a triangular shape rounded at the bottom, nothing near as classy as the picture. There was an arm that traversed the base and it had a little indicator wire.  I ordered front surface mirrors and filters and all the other odds-and-ends parts from various scientific hobby shops like Lafayette,  Esco Products, Radio Shack and others that advertised in Sky and Telescope Magazine.  My front surface mirror was mounted permanently to the arm axis and the see-through mirror was mounted midway on the body.  A peep hole eyepiece was set up in the back.  I arranged a number of sun filters to fit in front of the main mirror.

I had a little trouble setting up a graduated scale to calibrate my sextant.  Using a long string I arranged three equidistant poles in a field and placed the sextant on its side on one pole bringing the two other poles into overlap.  There was my 60 degrees from geometry.  I then did a Pythagorean calculation on a length of the string and moved one stick to form a 90 degree triangle.   With these measurements and a bunch of others I was able to build a graduated scale and glued it to the bottom of my sextant.

We lived in a place where there was no horizon so I made an artificial horizon, which is merely the reflection of the sun from a pan of water.  The reflection was half the distance.

I began shooting the sun.  I knew that Everett, Wa. was several degrees past our standard time meridian. Consulting the equation-of-time I calculated that the sum would reach my local time meridian a little late that time of year. On several days I took sun shots and tried to mark the angle every minute. Eventually I arrived at a latitude that was about one mile off and a longitude that was 7 miles off to the west right in the middle of Gardner Bay near Hat Island.  I considered this project finished and forgot all about it and moved on to other more interesting things. After all I was only 12.

But 70 years later it is fascinating to think about just what I had been able to do because of all the incredible amount of technology that has been developed over a long time to support these simple efforts.

Sources used:

Bown, Stephen R., Madness Betrayal and the Lash, 2008)
Bruton, Eric (the history of clocks, Orbis Publishing, 1979)
Jenkins, Martin (the time book, Martin Jenkins, 2009)
Cronin, John (the Marine Chronometer, Crowood Press, 2017)
Milham, Willis (Time & Time Keepers, Macmillan, 1923)
Sobel, Dava (Longitude, Walker, 1995)

So what did I just do?  I found my latitude and longitude and it was pretty easy.  Briefly here's how it was all done.  But before any part of this simple procedure was developed many other things had to be figured out, such as how to construct a grid over the surface of the earth and who would do it and how it would be designed.  If nobody moved anywhere there would be no need for maps, but mankind had a habit of moving constantly all over the planet.  Location became more and more critical especially for ships during the age of discovery (1500 to 1800). 

This all happened before GPS which we now casually take for granted but even GPS is based on a huge amount of science which was built up over a long period of time.

The first and foremost difficulty confronting navigation was the development of timekeeping, and even before accurate time could be considered a good calendar was needed.  A calendar involved much more than just counting days as discussed here but it involved an intricate knowledge of how the planet worked with the sun and understanding the movements.  A lot more science still was needed and in order to navigate the planet but having an accurate calendar was certainly the first step.

Keeping rough day to day time was easy by just observing the sun using sundials.  But the problems of navigation at sea presented a need for accurate timekeeping.  It is amazing that the first mechanical clock was invented in 1360 and it was another 400 years before any portable seaworthy clock was invented.

With the rise in sea power the nations of Europe had huge fleets and no good way to map the vast oceans.  Thus began the quest for the long sought after secret of Finding "The Longitude" as described in this essay.

A sudden increase in ocean going exploration beginning with Dias, Da Gama and Columbus created all kinds of accidents because of uncharted waters, poor navigational aids and no sea maps. Even good sailors ran into shoals and rocks.  Raging storms blew ships way off course, and they became lost in such huge seas.  Ships were woefully unprepared for months at sea where scurvy and other diseases tock their toll.  The five Magellan ships ran out of crew and only 17 sailors returned with one ship.  It was a sad beginning to ocean sailing. Full oceans were a lot bigger by far then the Mediterranean.

Even though good mariners could sail the Latitude,  "The Longitude" soon became a number one scientific problem to world navigation.

The Longitude