# Did early explorers really worry that they might fall off the edge of the world? **URL:** \ **Category:** Factual Questions\ **Created:** [November 15, 2008, 9:04am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838 "2008-11-15T09:04:05Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Bootis](https://avatars.discourse-cdn.com/v4/letter/b/e8c25b/32.png) [@Bootis](https://boards.straightdope.com/u/Bootis)\ **Post date:** [November 15, 2008, 11:36pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/21 "2008-11-15T23:36:46Z")
> [@Spiny\_Norman](#): > > Columbus’ challenge to the conventional wisdom of the time was his idea of the size of the Earth - and he was wrong. Does anyone know why Columbus insisted the earth was smaller than generally agreed upon by the knowledgeable? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [November 15, 2008, 11:47pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/22 "2008-11-15T23:47:57Z")
> [@Bootis](#): > > Does anyone know why Columbus insisted the earth was smaller than generally agreed upon by the knowledgeable? Yes, because he was a crank with a pet theory. Columbus theorized that it would be possible to reach Asia by sailing west. However, if the calculations of most people were correct, the distance was too far to be feasible to cover in the sailing vessels of that day. Columbus cherry-picked the available data to arrive at the conclusion that Asia was much much wider than most people believed, and that the circumference of the Earth was much smaller. This would make the distance to be sailed much shorter than it actually was, and possible to cover in the ships of the time. Coincidently, Columbus’s calculated distance to Asia was just about the distance to the Americas. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 12:14am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/23 "2008-11-16T00:14:53Z")
> [@Chronos](#): > > Which atomic scientists were those? All of the ones working on the Manhattan project knew that wasn’t possible. “…the nuclear physicists [at Los Alamos on July 13, 1945]…knew they were taking a giant step into the unknown. The warnings to the 509th [Composite Groupof the 313th Wing of the 21st Bombing Command of the 20th Air Force, i.e. the Enola Gay’s group] about lightning had not been fanciful. It was the one inponderable in equations. A stray bolt from an electrical storm could atomize all of them, and since the outer limits of a chain reaction were unknown, conceivably the entire planet might be destroyed. The weight of scientific opinion was against it, but no one could be sure.” –William Manchester, THE GLORY AND THE DREAM: A NARRATIVE HISTORY OF AMERICA, 1932-1972. Little Brown: Boston. 1974, pp. 376-7. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 12:22am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/24 "2008-11-16T00:22:30Z")
Manchester’s source for this paragraph seems to be Karl T. Compton’s article in the December, 1946 Atlantic Monthly. “If the Atomic Bomb Had Not Been Used.” ---
**Author:** ![Meltdown](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Meltdown](https://boards.straightdope.com/u/Meltdown)\ **Post date:** [November 16, 2008, 12:31am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/25 "2008-11-16T00:31:50Z")
There’s also [this](http://www.straightdope.com/columns/read/415/you-say-the-earth-is-round-prove-it): > [@](#): > > “The sphericity of the earth is proved by the evidence of … lunar eclipses,” Aristotle says. “For whereas in the monthly phases of the moon the segments are of all sorts–straight, gibbous [convex], crescent–in eclipses the dividing line is always rounded. Consequently, if the eclipse is due to the interposition of the earth, the rounded line results from its spherical shape” Not sure if “proved” is the same as “100% certain” – but it’s probably pretty close for someone like Aristotle. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [November 16, 2008, 1:25am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/26 "2008-11-16T01:25:03Z")
By 300 A.D., not only was the size of the Earth known pretty accurately, the size and distance of the sun and the moon had estimates that weren’t that far off. If the Greeks of 300 A. D. had had reasonably accurate naked-eye measuring equipment, they would have known the size and distance of the sun and moon pretty accurately. Even with lousy measuring instruments, they did halfway well: > **[On the Sizes and Distances (Aristarchus)](https://en.wikipedia.org/wiki/Aristarchus_On_the_Sizes_and_Distances)** > > On the Sizes and Distances (of the Sun and Moon) (Ancient Greek: Περὶ μεγεθῶν καὶ ἀποστημάτων \[ἡλίου καὶ σελήνης\], romanized: Perì megethôn kaì apostēmátōn \[hēlíou kaì selḗnēs\]) is widely accepted as the only extant work written by Aristarchus of Samos, an ancient Greek astronomer who lived circa 310–230 BCE. This work calculates the sizes of the Sun and Moon, as well as their distances from the Earth in terms of Earth's radius. > The book was presumably preserved by students of Pappus of Alexandr... The fact that the Earth, moon, and sun are spheres was thus not only known, but that fact was used in further calculations. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 16, 2008, 4:49am UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/27 "2008-11-16T04:49:23Z")
> [@](#): > > “…the nuclear physicists [at Los Alamos on July 13, 1945]…knew they were taking a giant step into the unknown. The warnings to the 509th [Composite Groupof the 313th Wing of the 21st Bombing Command of the 20th Air Force, i.e. the Enola Gay’s group] about lightning had not been fanciful. It was the one inponderable in equations. A stray bolt from an electrical storm could atomize all of them, and since the outer limits of a chain reaction were unknown, conceivably the entire planet might be destroyed. The weight of scientific opinion was against it, but no one could be sure.” It looks like this is warning that a lightning strike might trigger the bomb before it was released, and I don’t know enough about the devices to say whether that’s true. But there was already one tested at Trinity before they sent the bomber crews to Hiroshima and Nagasaki, and if there were any lingering doubt, that should have dispelled it. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 12:35pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/28 "2008-11-16T12:35:52Z")
> [@Chronos](#): > > It looks like this is warning that a lightning strike might trigger the bomb before it was released, and I don’t know enough about the devices to say whether that’s true. But there was already one tested at Trinity before they sent the bomber crews to Hiroshima and Nagasaki, and if there were any lingering doubt, that should have dispelled it. I think the date I was referencing was the date of the test at Trinity, when the lingering doubts (that lingered IOW up until July 12, 1945) still lingered, which was my (or Manchester’s) point: Until the thing had been done, there was always that shred of doubt. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 16, 2008, 12:44pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/29 "2008-11-16T12:44:56Z")
Paintings of Columbus and other sailors of his day often show them holding octants (similar to sextants), navigation instruments that were somewhat emblematic of the sailing profession. These instruments measure location on the earth by measuring the elevation of astronomical bodies above the horizon. They should only work if the earth is round. But I don’t think it’s obvious from the disappearance of tall items at the horizon as you move away from them that the earth is round (or more accurately convex, you’re right). The times I have looked for this, things always disappear in an increasingly hazy and indistinct horizon while they are also getting smaller overall. I’ve never been able to tell that the lower parts of objects were actually disappearing from view, as opposed to shrinking towards but never dipping below an ideal horizon. I think this proof of the convexity of the earth is too hard to observe unambiguously to be useful. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 1:02pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/30 "2008-11-16T13:02:41Z")
> [@pseudotriton\_ruber\_ruber](#): > > I think the date I was referencing was the date of the test at Trinity, when the lingering doubts (that lingered IOW up until July 12, 1945) still lingered, which was my (or Manchester’s) point: Until the thing had been done, there was always that shred of doubt. Yes, Trinity was 7/13/1945. The point about lightning is incidental–the more germane point here is that there remained a question even in Manhattan Project physicists’ minds that the A-bomb could set off a chain reaction that would destroy the planet. Even if only one or two of them (and Manchester implies that there were more) had doubts and fears, that’s well below 100% certainty that a chain reaction would not occur. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 16, 2008, 2:22pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/31 "2008-11-16T14:22:54Z")
> [@pseudotriton\_ruber\_ruber](#): > > Manchester’s source for this paragraph seems to be Karl T. Compton’s article in the December, 1946 Atlantic Monthly. “If the Atomic Bomb Had Not Been Used.” Compton’s [article is online](http://www.theatlantic.com/issues/46dec/compton.htm). He was not at the Trinity test and the piece says nothing about lightning or the risk of a runaway chain reaction. I haven’t read _The Glory and the Dream_, but the quoted passage seems a bit garbled. There was a thunderstorm the night before the Trinity test that led to worries about the tower being hit, but the real concern there was either a partial detonation or, more likely, the surrounding electrical equipment being fried, either of which would wreck the test. However, the 509th wasn’t running the test - and, offhand, I’m not even sure any of its members were present. (Various participants at Trinity did go on to join them on Tinian, but they were members of Los Alamos on secondment.) There had been a debate amongst the physicists about a bomb triggering a runaway chain reaction in the atmosphere several years earlier, but Hans Bethe quickly showed that this outcome was _exceedingly_ unlikely. Various people revisited the issue thereafter, but without overturning this basic conclusion. There is then some muttering in the hours before the test, but this is as much black humour as anything else. It’s true that nobody could be certain there was absolutely no risk, but there was agreement that it was acceptably minimal. It’s sometimes been suggested, including by Richard Rhodes, that Robert Serber was significantly concerned the night before, but he explicitly claimed in his memoirs _Peace & War_ (Columbia, 1998, p91) that his remarks at the time were jokes and that he thought there was no risk. Manchester’s remarks thus seem a garbled and exaggerated version of what actually happened - hardly an unknown occurance in that sort of popular history writing. Furthermore, none of this should be confused with the _popular_ perception in the Thirties that “splitting the atom” was somehow likely to end the world. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 2:41pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/32 "2008-11-16T14:41:21Z")
> [@bonzer](#): > > It’s true that nobody could be certain there was absolutely no risk, but there was agreement that it was acceptably minimal. I think “acceptably minimal” = “less than 100% certain,” and my point is that if you’re only 99% sure that you’re not starting something that will destroy the planet immediately, you’ve got a pretty large set of balls. To get back to the OP, if you’ve got that same level of confidence that you’re not going to sail off the edge of the planet into an endless abyss, I’ll give you points for being the first one to try it. As I read **Chronos** ’s assertions of 100% confidence, it was a completely settled issue, and the only problem was technological, not whether the outcome was achievable. I actually think the confidence level in both was less than 99% and the results have added to people’s assessment of their confidence before the fact, but even 99% takes considerable guts. Thanks for the link–I’ve always wanted to read Compton’s article. ---
**Author:** ![Superfluous\_Parentheses](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@Superfluous\_Parentheses](https://boards.straightdope.com/u/Superfluous_Parentheses)\ **Post date:** [November 16, 2008, 2:46pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/33 "2008-11-16T14:46:32Z")
> [@Napier](#): > > But I don’t think it’s obvious from the disappearance of tall items at the horizon as you move away from them that the earth is round (or more accurately convex, you’re right). The times I have looked for this, things always disappear in an increasingly hazy and indistinct horizon while they are also getting smaller overall. I’ve never been able to tell that the lower parts of objects were actually disappearing from view, as opposed to shrinking towards but never dipping below an ideal horizon. I think this proof of the convexity of the earth is too hard to observe unambiguously to be useful. Next time you’re at the beach on a clear day, look at the ships (esp large ships or sailing ships). On the sea, it’s really **very** obvious, and anyone who was familiar with ships at the time could have made the observation if he’d bothered to look. ---
**Author:** ![pseudotriton\_ruber\_ruber](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@pseudotriton\_ruber\_ruber](https://boards.straightdope.com/u/pseudotriton_ruber_ruber)\ **Post date:** [November 16, 2008, 3:00pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/34 "2008-11-16T15:00:09Z")
And Manchester wasn’t suggesting that the 509th was present at Trinity–just that they’d been given warning to avoid lightning storms on their test runs. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 16, 2008, 6:10pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/35 "2008-11-16T18:10:53Z")
I didn’t assert 100% confidence, because in science, there is no such thing. I can’t be 100% confident that I won’t accidentally destroy the world by scratching my nose. Despite a lack of 100% confidence, however, there is nonetheless a level of confidence beyond which one may say that one is certain of something. By the time of the Trinity test, all of the scientists involved were at that level of confidence. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [November 16, 2008, 6:16pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/36 "2008-11-16T18:16:10Z")
> [@Napier](#): > > Paintings of Columbus and other sailors of his day often show them holding octants (similar to sextants), navigation instruments that were somewhat emblematic of the sailing profession. I have never seen such a painting but if any exist they are inaccurate as the octant was invented a couple of centuries after Columbus. In Columbus’ time they used astrolabes and latitude could be determined by measuring the height of Polaris or by measuring the height of the sun above the horizon at the meridian crossing because tables of declination were already well known. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [November 16, 2008, 7:28pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/37 "2008-11-16T19:28:26Z")
> [@sailor](#): > > I have never seen such a painting but if any exist they are inaccurate as the octant was invented a couple of centuries after Columbus. In Columbus’ time they used astrolabes and latitude could be determined by measuring the height of Polaris or by measuring the height of the sun above the horizon at the meridian crossing because tables of declination were already well known. Columbus himself apparently never used even the astrolabe. His journal indicates he was unable to use his astrolabe on his first voyage, and there is no evidence he took one on any of his subsequent voyages. According to Morison in _Admiral of the Ocean Sea_ (p. 184), “The common quadrant … was the only instrument of celestial navigation that Columbus ever employed.” ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [November 16, 2008, 8:43pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/38 "2008-11-16T20:43:37Z")
> [@Chronos](#): > > I can’t be 100% confident that I won’t accidentally destroy the world by scratching my nose. You mean you’d do it _deliberately_? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 16, 2008, 8:49pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/39 "2008-11-16T20:49:18Z")
Aren’t quadrants, octants, and sextants all forms of astrolabe? In any event, the use of any of them to determine latitude requires the assumption that the Earth is round. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 16, 2008, 9:18pm UTC](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838/40 "2008-11-16T21:18:54Z")
\>Next time you’re at the beach on a clear day, look at the ships (esp large ships or sailing ships). On the sea, it’s really very obvious, and anyone who was familiar with ships at the time could have made the observation if he’d bothered to look. I HAVE done this. That’s why I posted what I have observed. I don’t know how good your eyes are and how clear the horizons you’ve seen are, but I spend a week on the Outer Banks every summer and have had a few other visits to various Eastern and Western US beaches, and I swear it’s never been clear that sailboats and other tall things moving toward or away from me are appearing or disappearing from the horizon up. I can’t tell that there’s a hull or a lower sail no longer visible while I can still tell there is an upper sail visible. Of course, I understand that that is what somebody ought to see if the air is clear enough (and if the gradient in air density is gradual enough, but that’s another story). The point here is that, for at least some frequent observers, the sailboat disappearing from the bottom up is not clear. And I’ve looked often and hard enough at water horizons to have seen a green flash once, and to have seen the sun rise over the Pacific twice (near Santa Barbara where the coast curves inward enough to allow this). [Previous page](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838.md?page=1) [Next page](https://boards.straightdope.com/t/did-early-explorers-really-worry-that-they-might-fall-off-the-edge-of-the-world/472838.md?page=3)