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Talk:Geocentric theory (view source)
Revision as of 17:53, November 6, 2008
, 17:53, November 6, 2008→Ptolemy's view of a stationary earth
::OTOH, he's well aware that "some astronomers propose a system in which the earth rotates roughly once a day from west to east, while the firmament stands still" (Aristarch's idea,BTW, whom he doesn't mention). Ptolemy goes to some length to show how ridiculous such an idea is. Similarly, he excludes an linearly moving earth.
::OTOH, he's well aware that "some astronomers propose a system in which the earth rotates roughly once a day from west to east, while the firmament stands still" (Aristarch's idea,BTW, whom he doesn't mention). Ptolemy goes to some length to show how ridiculous such an idea is. Similarly, he excludes an linearly moving earth.
::--[[User:BRichtigen|BRichtigen]] 14:34, 5 November 2008 (EST)
::--[[User:BRichtigen|BRichtigen]] 14:34, 5 November 2008 (EST)
But now, in the translation of ''R. Catesby Raliaferro'', the begin of Ch. 7 of the Book I of the '''Almagest''':
{{quotation|'''7. That the Earth Does Not In Any Way Move Locally'''
By the same arguments as the preceding [Ch. 5:'''That the Earth is in the Middle of Heavens'''] it can be shown that the earth can neither move in any one of the aforesaid oblique directions, nor ever change at all from its place at the centre. For the same things would result as if it had another position than at the centre. And so it also seems to me superfluous to look for the causes of the motion to the centre when it is once for all clear from the very appearances that the earth is in the middle of the world and all weights move towards it. And the easiest and only way to understand this is to see that, once the earth has been proved spherical considered as a whole and in the middle of the universe as we have said, then the tendencies and movements of heavy bodies (I mean their proper movements) are everywhere and always at right angles to the tangent plane drawn through the falling body's point of contact with the earth's surface. For because of this it is clear that, if they were not stopped by the earth's surface, they too would go all the way to the centre itself, since the straight line drawn to the centre of a sphere is always perpendicular to the plane tangent to the sphere's surface at the intersection on that line.
All those who think it paradoxical that so great a weight as the earth should not waver or move anywhere seem to me to go astray by making the judgment with an eye to their own effects and not to the property of the whole. For it would not still appear so extraordinary to them, I believe, if they stopped to think that the earth's magnitude compared to the whole body surrounding it is in the ration of a point to it. For thus it seems possible for that which is relatively least to be supported and pressed against from all side equally and at the same angle by that which is absolutely greatest and homogeneous. For there is no "above" and "below" in the universe with respect to the earth, just as none could be conceived of in a sphere. And of the compound bodies in the universe, to the extent of their proper and natural motion, the light and subtle ones are scattered in flames to the outside and to the circumference, and they seem to rush in the upward direction relative to each one because we too call "up" from above our heads to the enveloping surface of the universe; but the heavy and coarse bodies move to the middle and centre and they seem to fall downwards because again we all call "down" the direction from our feet to the earth's centre. And they properly subside about the middle under the everywhere-equal and like resistance and impact against each other. Therefore the solid body of the earth is reasonably consider as being the largest relative tho those moving against it and as remaining unmoved in any direction by the force of the very small weights, and as it were absorbing their fall. And if it had some one common movement, the same as that of the other weights, it would clearly leave them all behind because of its much greater magnitude. And the animals and other weights would be left hanging in the air, and the earth would very quickly fall out of the heavens. Merely to conceive such things make them appear ridiculous.
Now some people, although they have nothing to oppose to these arguments, agree on something, as they think, more plausible. And it seems to them there is nothing against their supposing, for instance, the heavens immobile and the earth as turning on the same axis from west to east very nearly one revolution a day; or that they both should move to some extent, but only on the same axis as we said, and conformably to the overtaking of the one by the other.
But it has escaped their notice that, indeed, as far as the appearances of the stars are concerned, nothing would perhaps keep things from being in accordance with this simpler conjecture, but that in the light of what happens around us in the air such a notion would seem altogether absurd. For in order for us to grant them what is unnatural in itself, that the lightest and subtlest bodies either do not move at all or no differently from those of contrary nature, while those less light and less subtle bodies in the air are clearly more rapid than all the more terrestrial ones; and to grant that the heaviest and most compact bodies have their proper swift and regular motion, while again these terrestrial bodies are certainly at times not easily moved by anything else - for us to grant these things, they would have to admit that the earth's turning is the swiftest of absolutely all the movements about it because of its making so great a revolution in a short time, so that all those things that were not at rest on the earth would seem to have a movement contrary to it, and never would a cloud be seen to move toward the east nor anything else that flew or was thrown into the air. For the earth would always outstrip them in its eastward motion, so that all other bodies would seem to be left behind and to move towards the west.
For if they should say that the air is also carried around with the earth in the same direction and at the same speed, none the less the bodies contained in it would always seem to be outstripped by the movement of both. Or if they should be carried around as if one with the air, neither the one nor the other would appear as outstripping, or being outstripped, by the other. But these bodies would always remain in the same relative position and there would b no movement or change either in the case of flying bodies or projectiles. And yet we shall clearly see all such things taking place as if their slowness or swiftness did not follow at all from the earth's movement.}}
(Ptolemy, Almagest, I, Ch. 7, translated by R. Catesby Taliaferro, "Great Books of the Western World", Encyclopaedia Britannica, 1952)
This should provide ample context... One can see the axioms of Ptolemy's physical understanding, like
*the heavier a body, the faster it falls
*the heaviest bodies are at the center of the universe, the lightest ones at its brim etc.
Dear R. Schlafly, while researching for this, I came across the blog ''Dark Buzz''. There, I got the impression that you have read the Almagest - and nothing of the above would be new for you. But then, I couldn't explain your statement: ''Assuming that this translation is accurate, it is possible that Ptolemy never even expressed an opinion about whether the Earth really goes around the Sun, or the Sun really goes around the Earth. He may have taken the completely correct position that he was modeling relative motion. '' Or did you just look at his ''Tetrabiblos''?
--[[User:BRichtigen|BRichtigen]] 12:53, 6 November 2008 (EST)