1

According to Wikipedia, there is no account of how the sphericity of the Earth was established. Though it goes on to say 'A plausible explanation is that it was "the experience of travellers that suggested such an explanation for the variation in the observable altitude and the change in the area of circumpolar stars, a change that was quite drastic between Greek settlements" around the eastern Mediterranean Sea, particularly those between the Nile Delta and the Crimea'

According to the same article the Sphericity of the Earth was widely accepted by the Greeks 5th century BCE. With Aristotle providing, what appears to me fairly flimsy arguments in 4th Century BCE, and more compelling evidence by Aristarchus in the 3rd BCE. This is quite a time-lapse, and hints at Aristarchus providing evidence for a theory already established. (A contemporary analogy would be Eddingtons expedition providing evidence for Einsteins theory of Gravitation - whose compelling physical idea was the equivalence of inertial & gravitational mass)

As the Greeks moved from a mytho-poetic cosmology to one focused on rational enquiry, were there general philosophical ideas that arose, and that would have proposed and made convincing the case for a spherical Earth?

Mozibur Ullah
  • 1
  • 14
  • 88
  • 234
  • 1
    The *title* of this question looks to be a historical one, better asked on [History.SE]. The *body* of this question looks like an *answer* to another question, or perhaps a blog post. That is to say, you appear to be making an argument, rather than asking a question. If this not a purely historical question (as your title might suggest), then please consider [editing](http://philosophy.stackexchange.com/posts/2638/edit) to make more explicit what your *specific philosophical question* is. Often times, good questions will end with a summary of what is being asked. – Cody Gray - on strike Apr 20 '12 at 02:28
  • ok, I'll think about it. – Mozibur Ullah Apr 20 '12 at 02:34
  • 3
    "philosophical ideas"? I don't think any philosophers determined the Earth was spherical purely through *a priori* reasoning.... if you mean "scientific ideas" (*a posteriori*) then this is probably better fit for history, as that would cover **history of science**. – stoicfury Apr 20 '12 at 19:43

1 Answers1

4

As the Greeks moved from a mytho-poetic cosmology to one focused on rational enquiry, were there general philosophical ideas that arose, and that would have proposed and made convincing the case for a spherical Earth?

Yes: observation. The sight of ships appearing on the horizon (masts first) makes the curvature of the earth evident. I think a better question would be why any culture situated adjacent to an ocean or a sea of sufficient size would ever believe the earth to be anything but curved. Furthermore, as you point out, for a sea-faring people (or a widely travelling land-based people), the celestial evidence is highly suggestive.

Michael Dorfman
  • 23,267
  • 1
  • 44
  • 69
  • 2
    "observation philosophy" = looking at curves and not calling them flat? XD – stoicfury Apr 20 '12 at 19:46
  • I don't find that convincing enough. Couldn't you just have a curved flat Earth? After all the Earth itself is not perfectly flat. Other cosmological systems had a bowl, why not an inverted bowl? – Mozibur Ullah Apr 22 '12 at 05:46
  • 1
    Some systems did have an inverted bowl. In the absence of evidence to sway things one way or the other, I suppose it came down to which explanation seemed more fitting. The point being, as they moved to a cosmology focused on rational enquiry, they adapted the cosmology to fit with their observations. – Michael Dorfman Apr 22 '12 at 09:53
  • @dorfman: I know Aristotle made the same argument you stated, but I'm sceptical of the sail of a boat appearing first on the horizon. Imagine a boat with a square sail, say 20 metres high, with a hull say of 2 metres showing above the sea, how reliable is an observation going to be when said boat is 2 km away. The boat would appear to the eye as a cm in height. The kind of arguments I was thinking of are: – Mozibur Ullah Apr 24 '12 at 16:56
  • 1. is the earth limitless in extent? Suppose not, then it must end in all directions, including *beneath* us. In which case we have the earth hanging in space. – Mozibur Ullah Apr 24 '12 at 16:56
  • 2. The Sun, the moon also hang in space. They are round. Perhaps then the Earth is also round. – Mozibur Ullah Apr 24 '12 at 16:59
  • 3. The sphere is the *perfect* 3-dimensional shape. So its more likely that these bodies are not disks but spheres, and this still fits in with observation. – Mozibur Ullah Apr 24 '12 at 17:01
  • 4. A material conception of cosmology: Where does the Sun go? In ancient Egyptian Cosmology, Ra the sun god would cross the sky in a boat, only to return to his starting point in the underworld. This shows some reasoning going on: they're not postulating a *new* Sun each day, and that it must *return* to its starting point. Going to a wholly material cosmology, the Sun going around the Earth fits in with observation & point 1. – Mozibur Ullah Apr 24 '12 at 17:06
  • 5. Once you get to this point, then there is additional supporting evidence: the solar/lunar eclipse, and gravity: all matter tends to the centre, and by symmetry the shape will be a sphere. I think Aristotle makes these two arguments. – Mozibur Ullah Apr 24 '12 at 17:15
  • 6. Then there is the question of size: Are the three bodies, the Sun, the Earth & the moon of the same size? Again going from mythology when the sun god was seen as greater than the earth goddess (the change in gender is significant), I'd suggest some would have stated that the Sun was greater & therefore larger. Now the smaller body should go around the greater body: So we have the earth going around the Earth – Mozibur Ullah Apr 24 '12 at 17:20
  • Now, I realise all this is conjectural, but it isn't completely implausible, and I'd hold that arguments of this type would have been made at that point. – Mozibur Ullah Apr 24 '12 at 17:23
  • @MoziburUllah: I live on the ocean, and I see boats coming in several times a day. The fact that they come masts first is clearly visible to someone with ordinary eyesight. Your other conjectures seem relatively plausible to me (except the sixth, which strikes me as weak.) – Michael Dorfman Apr 24 '12 at 18:58
  • I defer to you observational skill. 6 is not as strong as the others, but I think it plausible the question of size would occur, and the idea of the smaller going round the larger is more natural. The only question then being determining which is actually the larger, and there my argument doesn't amount to much. Aristarchus did determine the sun was larger, and wikipedia suggest this might have led him to proposing the heliocentric model. – Mozibur Ullah Apr 24 '12 at 23:49