Aristotle, in Book I, text #44 of <i>De Caelo</i> [273a9-13], says that if one of two contraries is delimited it is thus necessary that the other be delimited as well; and because the center, which is the limit of downward motion, is limited, it is necessary that upward [motion] itself be delimited . </s>
<s id="id.5.0.35.00.02">And the same thing is concluded from text #58 [274b9-15]: {1} read {2} the text. </s>
</p>
</subchap2>
<subchap2>
<p>
<s id="id.5.0.36.00.00"/>
<s id="id.5.0.36.00.01">Aristotle, in Book I, text #51 of <i>De Caelo</i> [273b32-274a2] {1} says, Speed is to speed as heaviness is to heaviness. </s>
</p>
</subchap2>
<subchap2>
<p>
<s id="id.5.0.37.00.00"/>
<s id="id.5.0.37.00.01">Aristotle, by text #89 of Book I, of <i>De Caelo</i> [277a33-277b2], shows that things that are moved naturally are not moved by force and through extrusion. {1} </s>
</p>
</subchap2>
<subchap2>
<p>
<s id="id.5.0.38.00.00"/>
<s id="id.5.0.38.00.01">Aristotle, in Book I, text #96 of <i>De Caelo</i> [278b14-15], writes: For as a rule we have called the outermost thing and what is uppermost the heaven. </s>
<s id="id.5.0.38.00.02">And in text #21 [270b6-8] he says: And the place which is above that is assigned to God. {1}</s>
</p>
</subchap2>
<subchap2>
<p>
<s id="id.5.0.39.00.00"/>
<s id="id.5.0.39.00.01">Things that are moved upward, go up more violently than naturally: for ascent has an external cause, but descent an internal one. </s>
</p>
</subchap2>
<subchap2>
<p>
<s id="id.5.0.40.00.00"/>
<s id="id.5.0.40.00.01">Aristotle, in Book I, text #5 of <i>De Caelo</i> [268b21-22], says: Now I call upward what is away from the center, but downward what is toward the center. {1}</s>
</p>
</subchap2>
</subchap1>
</chap>
<chap>
<subchap1>
<subchap2>
<p>
<s id="id.6.0.0.00.00"/>
<s id="id.6.0.0.00.01">[Program of a work on motion]{1}</s>
</p>
<p>
<s id="id.6.0.0.01.00"/>
<s id="id.6.0.0.01.01">It may be asked whether heavy things are truely moved toward the center; on this, Ptolemy, <i>Almagest</i>, Book I, chapter 7. </s>
</p>
<p>
<s id="id.6.0.0.02.00"/>
<s id="id.6.0.0.02.01">Whether the impressed force will be consumed by time or by the heaviness of the mobile. </s>
</p>
<p>
<s id="id.6.0.0.03.00"/>
<s id="id.6.0.0.03.01">By what natural motion takes place. </s>
</p>
<p>
<s id="id.6.0.0.04.00"/>
<s id="id.6.0.0.04.01">By what violent motion takes place. </s>
</p>
<p>
<s id="id.6.0.0.05.00"/>
<s id="id.6.0.0.05.01">Whether a medium is necessary for motion. </s>
</p>
<p>
<s id="id.6.0.0.06.00"/>
<s id="id.6.0.0.06.01">Whether the purely and simply heavy and purely and simply [light {1}] are given. </s>
</p>
<p>
<s id="id.6.0.0.07.00"/>
<s id="id.6.0.0.07.01">Whether the elements in their proper place are heavy or light. </s>
</p>
<p>
<s id="id.6.0.0.08.00"/>
<s id="id.6.0.0.08.01">Concerning the ratio of motions of the same mobiles in different media. </s>
</p>
<p>
<s id="id.6.0.0.09.00"/>
<s id="id.6.0.0.09.01">Concerning the ratio of the motions of different mobiles in the same medium. </s>
</p>
<p>
<s id="id.6.0.0.10.00"/>
<s id="id.6.0.0.10.01">Concerning the cause of the slowness and the speed of motion. </s>
</p>
<p>
<s id="id.6.0.0.11.00"/>
<s id="id.6.0.0.11.01">Whether there a rest at the turning point. </s>
</p>
<p>
<s id="id.6.0.0.12.00"/>
<s id="id.6.0.0.12.01">Whether natural motion is always intensified, and why it is intensified. </s>
</p>
<p>
<s id="id.6.0.0.13.00"/>
<s id="id.6.0.0.13.01">Whether the slowness and the swiftness of natural motion is due to the rareness or the de....of the me.... .</s>
</p>
<p>
<s id="id.6.0.0.14.00"/>
<s id="id.6.0.0.14.01">In motion 3 things are considered: the mobile, the medium, and the mover.</s>
</p>
<p>
<s id="id.6.0.0.15.00"/>
<s id="id.6.0.0.15.01">How the form of mobiles helps or hinders motion. </s>
</p>
<p>
<s id="id.6.0.0.16.00"/>
<s id="id.6.0.0.16.01">Concerning the ratio of the heavinesses of the same heavy thing in different media, on which depends the question of the ratio of its motions. </s>
</p>
<p>
<s id="id.6.0.0.17.00"/>
<s id="id.6.0.0.17.01">Given the heaviness of the medium and the speed of the mobile, is also given the heaviness of the mo.... .</s>
</p>
<p>
<s id="id.6.0.0.18.00"/>
<s id="id.6.0.0.18.01">Given the heaviness of the mobile and of the medium, the speed of motion is given. </s>
</p>
<p>
<s id="id.6.0.0.19.00"/>
<s id="id.6.0.0.19.01">Given the speed and the heaviness of the mobile, the heaviness of the medium is given. {1} </s>
<s id="id.6.0.0.21.01">One must consider the ratio of motions on different inclined planes, and whether perchance lighter things go down more swiftly at the beginning; just as in the balance, the smaller the weights, the more easily the motion takes place. </s>
</p>
<p>
<s id="id.6.0.0.22.00"/>
<s id="id.6.0.0.22.01">The medium retards natural motion in the following manner: as, when a bell goes down, it is so to speak a solid body consisting of air enclosed .... by the metal, and because of this it is lighter than if air were not present. </s>
</p>
<p>
<s id="id.6.0.0.23.00"/>
<s id="id.6.0.0.23.01">Lighter mobiles are moved more easily, as long as they are linked.... to what moves them; but, outside the hand of the mover, ....[they conserve] for a short time the impetus.... .</s>
</p>
<p>
<s id="id.6.0.0.24.00"/>
<s id="id.6.0.0.24.01">The argument of those who say that motion is accelerated at the end since.... {1} .</s>
<s id="id.6.0.0.24.01.end">End see my notes below.</s>
