MobileRead June 2017 Discussion: Longitude by Dava Sobel (spoilers)

[crich70]

Originally Posted by CRussel

Without getting political, one of the important points this book makes about science is the need to address what is, not what you expect/want it to be. The scientific method is about observing and addressing the results of your experiment, not about trying to twist the facts to fit a pre-conceived notion. I did NOT think it was about elite v. working class, though that certainly entered in to it, but much more about trying to shape the facts to fit the required result.

Part of that (I think) seems to have been that they had preconceptions of how the Longitude problem would be solved. The Astronomers assumed that the method would involve using the stars (the celestial clock) and that it was impossible to construct a mechanical clock that was accurate enough for the job. Of course back then the technology didn't exist (prior to Harrison) to make such a clock. We still have the problem today of thinking that because something hasn't been done it probably can't be.

[issybird]

Originally Posted by CRussel

Without getting political, one of the important points this book makes about science is the need to address what is, not what you expect/want it to be. The scientific method is about observing and addressing the results of your experiment, not about trying to twist the facts to fit a pre-conceived notion. I did NOT think it was about elite v. working class, though that certainly entered in to it, but much more about trying to shape the facts to fit the required result.

Great insight, Charlie! I'll elaborate, if I may, that it's thus the problem that factions get invested in particular theories and methods and double down (to use the current cant phrase) when challenged. While scientists now espouse the scientific method as they did not necessarily do in the 18th century, we still have ample evidence of the behavior in other spheres today.

[crich70]

Originally Posted by issybird

Great insight, Charlie! I'll elaborate, if I may, that it's thus the problem that factions get invested in particular theories and methods and double down (to use the current cant phrase) when challenged. While scientists now espouse the scientific method as they did not necessarily do in the 18th century, we still have ample evidence of the behavior in other spheres today.

Even in science we still see it. Einstein and his constant is an example from more recent history. His equations showed that the universe is expanding so he introduced an extra to cancel that out because he didn't want to believe it. Then Hubble showed that in fact the universe is expanding (by the color shift of stars) which shows that even very intelligent scientists can still make errors.

[CRussel]

One thing I found interesting is the amount of complicated mathematical calculations required to use any of the astronomical methods of determining longitude. Before Maskalyne's tables were published the process took hours and hours, and was, even with the tables, subject to error and miscalculation. But even more importantly, required a mathematical skill that wasn't necessarily to be found with every naval captain! The beauty of the chronometer method enabled by Harrison's watches was that the calculation took a matter of minutes, was not nearly so subject to error, and didn't require complex, advanced mathematical calculations.

[crich70]

Originally Posted by CRussel

One thing I found interesting is the amount of complicated mathematical calculations required to use any of the astronomical methods of determining longitude. Before Maskalyne's tables were published the process took hours and hours, and was, even with the tables, subject to error and miscalculation. But even more importantly, required a mathematical skill that wasn't necessarily to be found with every naval captain! The beauty of the chronometer method enabled by Harrison's watches was that the calculation took a matter of minutes, was not nearly so subject to error, and didn't require complex, advanced mathematical calculations.

And was so simple you could explain it to someone/anyone in a few moments. Not something you could do with Maskalyne's tables I'm thinking.

[CRussel]

Originally Posted by crich70

And was so simple you could explain it to someone/anyone in a few moments. Not something you could do with Maskalyne's tables I'm thinking.

No, not even once the heavy lifting of Lunars had been done by tables, they were still far more complex. And remember that those tables weren't published until well after Harrison's clocks had amply demonstrated to an unbiased mind (if one could have been found) that they could and did solve the problem simply and quite elegantly.

The one real caveat of the Harrison clocks, and their immediate successors, was the cost and time to create. It was quite a while before the price came down to something that could reasonably be afforded by a seagoing captain. And even when the price got down to somewhere below £100, it was still more expensive than a Rolex of today.

[Dazrin]

Originally Posted by crich70

And was so simple you could explain it to someone/anyone in a few moments. Not something you could do with Maskalyne's tables I'm thinking.

Right! It only took 1 paragraph for me to understand the clock method, you still need to determine your latitude but that was much easier to do.

The two clock times enable the navigator to convert the hour difference into a geographical separation. Since the Earth takes twenty-four hours to complete one full revolution of three hundred sixty degrees, one hour marks one twenty-fourth of a spin, or fifteen degrees. And so each hour’s time difference between the ship and the starting point marks a progress of fifteen degrees of longitude to the east or west. Every day at sea, when the navigator resets his ship’s clock to local noon when the sun reaches its highest point in the sky, and then consults the home-port clock, every hour’s discrepancy between them translates into another fifteen degrees of longitude. Those same fifteen degrees of longitude also correspond to a distance traveled. At the Equator, where the girth of the Earth is greatest, fifteen degrees stretch fully one thousand miles. North or south of that line, however, the mileage value of each degree decreases. One degree of longitude equals four minutes of time the world over, but in terms of distance, one degree shrinks from sixty-eight miles at the Equator to virtually nothing at the poles.

[crich70]

So basically you simply add or subtract the difference in time (east or west) and then depending on your latitude you figure that you have traveled distance x since the same time the day prior. It must have made land charting a bit easier as well. You could trust that you were at a given place rather than just your best guess as to your position like in earlier maps.

[CRussel]

Originally Posted by crich70

So basically you simply add or subtract the difference in time (east or west) and then depending on your latitude you figure that you have traveled distance x since the same time the day prior.

Nearly that simple. You go through the longitude to get to the distance, though, since the longitude is actually more important. Your latitude is determined by the angle of a known star, the moon, or sun above the horizon and by the 1730s, this was measured using a sextant. (Many commercial captains today still use one regularly, even though GPS is far more precise. But then, I've been known to use a slide rule in recent memory. ) Your longitude is determined by the difference in local noon v. Greenwich Mean Time noon.

The problem comes when you can't get a reliable sighting to determine exact local noon, or your latitude. Then you're down to dead reckoning, using the speed of the ship (literally done by tossing a weighted line over the side of the ship, and counting the number of knots in the rope in a given time), the compass heading, and a guess of the amount of current and "leeway" the ship is making.

[issybird]

Originally Posted by CRussel

But then, I've been known to use a slide rule in recent memory.

I once had a boss who still used a slide rule. Much faster, he said, and of course that was true.

[CRussel]

Good luck trying to buy a new one these days. However, it appears there's a thriving secondary market on eBay for them, with Versalog 1460s going for anywhere from $20-$45 USD. I'm tempted to buy one, actually.

[crich70]

Originally Posted by CRussel

Nearly that simple. You go through the longitude to get to the distance, though, since the longitude is actually more important. Your latitude is determined by the angle of a known star, the moon, or sun above the horizon and by the 1730s, this was measured using a sextant. (Many commercial captains today still use one regularly, even though GPS is far more precise. But then, I've been known to use a slide rule in recent memory. ) Your longitude is determined by the difference in local noon v. Greenwich Mean Time noon.

The problem comes when you can't get a reliable sighting to determine exact local noon, or your latitude. Then you're down to dead reckoning, using the speed of the ship (literally done by tossing a weighted line over the side of the ship, and counting the number of knots in the rope in a given time), the compass heading, and a guess of the amount of current and "leeway" the ship is making.

Dead reckoning is probably the method the Admiral was using in 1707 when the fleet of ships were wrecked. It sounds like you really needed both your latitude and longitude to be accurate or you were in deep trouble. And what form that trouble took could vary depending on where you were. It can't have been easy to live the life of a seaman back then.

[CRussel]

There's a reason they call it dead reckoning, unfortunately.

[Dazrin]

I have now read 4 of the books that were nominated for June and I think we ended up with one of the better ones, both for discussion and for quality.

Gulp is a lot of fun and well written but a bit hard to stomach sometimes; I'm also not sure how good the discussion would have been. Astrophysics for People in a Hurry is a VERY high level primer, as it was intended, but that didn't translate into a great book for me. Overall, I like hearing NGT talk more than I like his writing. What If? is also a lot of fun but I am not sure it would have lead to great discussion.

[ekbell]

I enjoyed reading Longitude but it suffered a bit from being read shortly after Sextant by David Barrie which covers the invention of the sextant and advances of navigation while also looking at the marine surveyors of the late 18th and early 19th centuries.