how many and how great are the difficulities that this solution involves. </s>
<s id="id.1.2.9.01.05">In the first place, who is ignorant of the fact that air in its own region is neither heavy nor light, {1}and that therefore it is carried neither upward nor downward? </s>
<s id="id.1.2.9.01.06">For this has been demonstrated above. {1}</s>
<s id="id.1.2.9.01.07">Secondly, if the speed of the motion of the mobile follows its heaviness, as everyone wants, and the sphere of lead has earth and water in place of the parts of air which there are in the woodden sphere, and earth and water are heavier than air, as we can readily believe, will not the lead be heavier, and will it not go down faster? </s>
<s id="id.1.2.9.01.08">And as for what they say about iron and lead, in order to show that air exerts weight, if lead is heavier because it has more air, then wood will be heavier than both iron and lead, since it is has more air than each one of them. </s>
<s id="id.1.2.9.01.09">Thirdly, if the great quantity of air which is in wood makes it faster, then it will always be moved faster, as long as it is in air. </s>
<s id="id.1.2.9.01.10">Yet experience shows the contrary: for it is true that wood at the beginning of its motion is carried more speedily than lead; but a little later the motion of lead is so accelerated that it leaves the wood behind, and, if they are released from a high tower, the lead gets ahead of it by a large distance: and I have often put this to the test. {1}</s>
<s id="id.1.2.9.01.11">Consequently we must try to draw a sounder cause from sounder hypotheses.</s>
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<p>
<s id="id.1.2.9.02.00"/>
<s id="id.1.2.9.02.01">Oh, how easily are true demonstrations derived from true principles. </s>
<s id="id.1.2.9.02.02">If it is true, as we have said {1}, that mobiles, as they recede from a state of rest, recede with an amount of contrary impressed force equal to their heaviness, then those that are heavier will recede in conjunction with a greater contrary force: but if heavier ones must consume more force impelling them in the contrary direction, it will surely be necessary that heavier mobiles are moved more slowly, since they undergo a greater resistance. </s>
<s id="id.1.2.9.02.03">And if, on the other hand, these things are true, it follows that heavier things, after they have consumed so much of the contrary resistance that they are no longer hindered by as much as lighter things are, must go down more speedily: which, again, experience surely shows.</s>
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<p>
<s id="id.1.2.9.03.00"/>
<s id="id.1.2.9.03.01">But then again one must not silently pass over a great difficulty that arises here</s>
<s id="id.1.2.9.03.02">For, though heavier mobiles have more of the contrary quality to consume than lighter mobiles, yet they also have a greater heaviness, with which they can destroy it; since this is so, it seems reasonable that they should be moved at the beginning only at equal speed: and the cause </s>
