Friday, November 24, 2006

Flight of the Navigator Part II

Cue music: Dean Martin, That's Amore
"When the Moon hits your Eye like a big pizza pie, That's Amore"

In the last installment, I established that the pre-chronometer method of determining longitude was the "method of lunar distances" and that it was used by the major navies of the world up until the nineteenth century. Before that method could come into use, however, a comprehensive catalog of lunar, solar, and stellar observations bases had to be established and the mathematics of using that catalog had to be instilled in the sailors and navigators of those navies. That math was worked out in the twenty to seventy centuries before modern chronometers. So was the shorthand that made it possible to cram all that information into a concise form that a ship's navigator could take with him on a voyage. That shorthand and its rendering migrated to a small host of activities, both related and unrelated to navigation. Astronomers probably used it first, then sailors, and finally, astrologers and alchemists came long after the sailors got ahold of it. Both the math and the shorthand were lost and regained several times over that long period, but not necessarily both at the same time and also not necessarily by all users at once.

Throughout that time (and still today) the "back up" method for estimating longitude is "dead reckoning". That method depends on much simpler math than does lunar distances. It is also much more prone to error.

Also in the the last installment, I established that to the celestial navigator, the sky is pre-Copernican, that the Earth is the axis around which the heavens rotate.

Axis. Rotation. Wheel. Arcs. Spokes. .... all leading to geometry and trigonometry. And, more importantly within this discussion, leading to tools with which to measure angles.

I closed the last installment asking "Where are the tools? Who used them? And where did they use them?" I should have added two more questions: "Where did they get them?" and "How did they use them?"

First things first

The first thing we have to establish is that the ancients actually had these tools and knew how to use them. In order to do that I have to draw upon the work and accepted findings of history, archeo-astronomy, and archeology.

The star we call Polaris was not always our "pole" star. The Earth's axis "wobbles " over time (long periods in human terms, a mere blink in geologic time). In fact, Polaris is not a perfect match to the axis even today, but has a slight angle from "true" north. Four or five thousand years ago, Polaris was just another star, not "the" guiding light upon which all navigators depended. A different star served that purpose back then. For purposes of this discussion, it doesn't really matter which star it was, as long as there was one. And there definitely was one that sailors and land navigators alike used to orient themselves and to navigate to far flung places.


Enter Pytheas, the Ancient Greek Navigator.

"He traveled around a considerable part of Great Britain, circumnavigating it between 330 and 320 BC. Pytheas is the first person on record to describe the Midnight Sun, the aurora and Polar ice, and the first to mention the name Britannia and Germanic tribes. ... Pytheas estimated the circumference of Great Britain within 2.5% of modern estimates."

The estimate of circumferance of the British Isles being that close would be a pretty clear indication that Pytheas did not use dead reckoning. Furthermore, there is clear evidence in the ancient manuscripts of Pliny the Elder and others, that Pytheas navigated the far reaches of the North Sea and some indication he also ventured as far as Iceland or perhaps beyond it. His own account is lost, but the content was repeated by other writers for several centuries. He also recorded for the first time the name "Thule" as an island of the north. Some scholars speculate that it was Iceland. If that speculation is true, then Iceland was inhabited long before modern scholars think it was. He also may have visited Orkney, the Faroes, and Norway. All in the fourth century B.C.

At the time of Pytheas' voyage, Greece had a colony at present day Marseilles and the Strates of Gilbraltor was blockaded by the Carthegenians, so Pytheas either ran the blockade or first travelled overland to Marseilles to set sail from there. There was a real reason the Greece had a colony there: Tin.


"The first account of Cornwall comes from the Sicilian Greek historian Diodorus Siculus (c.90 BC–c.30 BC), supposedly quoting or paraphrasing the fourth-century BC geographer Pytheas, who had sailed to Britain:

[The inhabitants of that part of Britain called Belerion or the Land's End] from their intercourse with foreign merchants, are civilised in their manner of life. They prepare the tin, working very carefully the earth in which it is produced…Here then the merchants buy the tin from the natives and carry it over to Gaul, and after travelling overland for about thirty days, they finally bring their loads on horses to the mouth of the Rhône.

"Who these merchants were is not known. There is no evidence for the theory that they were Phoenicians."

"Caesar was the last classical writer to mention the tin trade, which appears to have declined during the Roman occupation"

I'll take to task the statement that "there is no evidence for the Phoenicians" in another installment, but this is about Pytheas' ability to navigate and the reasons for his voyage. Besides the indications of his travelling to the far north, he also seems to have sailed far into the Baltic. Could he have been trying to find another sea route to the tin mines, a way around the Carthegenian blockade? Or did he undertake such an adventure purely for exploration?

We may never know the answer to that one, but there are a few points worthy of review:
  1. Pytheas sailed into or at least interveiwed someone who had sailed into the Arctic Ocean (Midnight Sun, sea slush/polar ice, Aurora, etc.). The only thing missing is mention of white bears.
  2. Pytheas most likely followed the overland tin route from Athens to the coast of present day France. The tin route was millenia old on both land and sea in his time.
  3. Pytheas was able to estimate distances at sea and the extent of land masses with uncanny precision.
  4. Subsequent historians cited his work for several centuries to come.
Could Pytheas have sailed all those seas and recorded those travels with such precision without the tools of a navigator? Not likely. Even if he did so using only dead reckoning, then he was still a master navigator and had to understand the trigonometry. It's also interesting that the 2.5% error is roughly equal to the error between using plain trigonemetry versus spherical trigonometry to ascertain the circumference of the British Isles. Either way, he had to use one or the other form of the math to do it and he had to measure the angles. Even to dead reckon his way around Britain, he had to measure the angle from north, that is, from a pole star. To do that, he had to have the tools to measure the angles.

But Pytheas is only one historical figure!!

The point exactly. Or, at least, part of it. He was a verifiable figure from history who navigated well beyond the Mediteranean in a time when the "known world" was limited to a much smaller place than he travelled. There were others who undertook similar ventures at different times, but his is probably the best documented voyage (i.e., cited by later historians) in antiquity and his story contains the most verifiable information, free of any dissenting or contradictory claims. The rest of the point in citing his story is that he had to have the tools to navigate and had to understand their use. What tools, specifically, did he use? We have no evidence of a specific design, because his account, his " ship's logs", is lost, not available to us (it probably went "poof" with the rest of the library at Alexandria). And, although somewhat speculative, it seems quite likely that the voyage was initiated with some regard to the tin trade in support of the bronze industries of his time.

The only thing lacking, so far, in proving that Pytheas and other figures in antiquity had and used the tools to measure longitude is the maps they would have made. I'll come back to that and the shorthand that encoded those maps in the Part III.

Holy double crosses, Batman!! Who sent Pytheas on a slow boat? Or was that "goat"?

Stay tuned...

No comments: