BİRİNCİ FEN · ÜÇÜNCÜ BÂB · DOKUZUNCU FASIL · Sekizinci Madde
**Article Eight: Responding to Objections Regarding New Astronomical Knowledge Based on Natural Principles**
Know, esteemed one, that objections have been raised against the new astronomical knowledge based on natural principles, and responses to them are as follows. The lowest place is the center of the universe. Therefore, it is fitting and necessary for the earth, being the heaviest body and situated at the lowest place – the center of the universe – to remain stationary. Were it not so, but rather if the earth were in motion, this would certainly be felt; buildings and trees would collapse with their heads downward, and heavy objects could not fall straight down from above.
For (those aforementioned heavy objects) traveling in a straight line would reach points that have moved along with the surface of the earth. For example, birds flying in the air would have their nests carried away by the earth, and they would be unable to find them again. Furthermore, the motion of a round object thrown westward would clearly slow down compared to its being thrown eastward. An arrow shot westward would travel a greater distance than one shot eastward, because as the arrow travels west, it is met by the surface of the earth moving from west to east, thus increasing the distance covered and diminishing its speed.
The individual responses to these objections are as follows: Is the earth indeed the lowest place? This is not yet an established or clarified matter. However, the evidence presented in support of this claim has been rejected. Moreover, regarding the nature (mizac) of the earth, it is not yet definitively known whether it is heavier than other stars. Perhaps their being above and below has also been observed relative to the earth. Although heavy objects and large masses of stone return to the ground when they are separated from it, this does not preclude the earth, as a heavy body, from moving from its place.
And in response to (the aforementioned objections), it is said: We are enveloped within the earth and that soft matter, like a water eddy, and therefore we do not feel the earth’s motion; nor is it due to this that buildings and trees do not fall over or become uprooted. Perhaps it is from this evidence that one can infer that objects remain standing and fixed. Whether the earth is stationary or moving along with that aforementioned soft matter, there is no impediment to heavy objects falling straight down. For it is certain that the falling of a heavy object is influenced not only by its own motion but also by the motion of that soft matter. This truth is exemplified by the stone thrown from the deck of a ship [100/b]. For whether the ship is at rest or in motion, when the stone is thrown downwards, it falls to the bottom of the hold as experience demonstrates. The movement of the ship contributes to this process. Perhaps the true nature of the matter is that neither the fall of a heavy object nor the descent of that stone is strictly linear; rather, it occurs along a curved path.
According to our observation, if one imagines a vertical line within a ship, this imagination resembles the following: When a stone is thrown from the deck of a ship to its hold, it appears to descend in a straight line when viewed from within the ship. However, to those observing from outside the ship – that is, from the sea – two movements are perceived in the stone; one movement shows it falling vertically downwards, and the other demonstrates its descent in accordance with the ship’s motion. Thus, these two movements trace out a curved line. Just as fish benefit from the movement of water, so too do birds take advantage of the air's movement, preventing them from straying far from their nests. The motion of a round object thrown eastward is not particularly swift compared to others. Furthermore, the distance an arrow travels when shot westward is no greater than that of one shot eastward.