276 for it would not be carried either upward or downward: hence the heaviness of a in water also would be zero, if in air it were as 4. But since in air it is 8, in water it will be 4: and, for the same reason, the heaviness of b in water would be 2: for which reason their heavinesses would be in a ratio of 2/1, just as the swiftnesses of the motions. And one must proceed by similar reasoning concerning the light.And the conclusion is drawn that, given the heavinesses of the two weights in air, immediately their heavinesses in water can be known: for once the heaviness of an amount of water as great in size as the sizes of the weights has been subtracted from each of them, their heavinesses in water will remain. And similarly with other media. And, from what has been said, it can be manifest to anyone, that we have of no thing its own proper heaviness {1}: for if, for example, two weights are weighed in water, who will say that the heavinesses that we will see then are the true heavinesses of these weights, whose heavinesses, when the weights are weighed in air, will show themselves to be different from these, and will observe with one another another ratio?
If again they could be weighed in another medium, for example, fire, the heavinesses would again be different, having to one another another ratio: and in this way they will always vary, according to the difference in the media.
And if they could be weighed in the void, in this case surely, where no heaviness of the medium would diminish the heaviness of the weights, we would perceive their exact heavinesses. But since the Peripatetics, with their leader, have said, that in the void no motions can come about, and consequently that all things weigh equally, perhaps it will not be inappropriate to examine this opinion, and to consider with care its foundations and its demonstrations: for this question is one of those that have to do with motion. Chapter 10 [276.24-284.29]Where, against Aristotle, it is demonstrated that, if there were a void, motion [in it] would not happen in an instant, but in time. {1}
Aristotle, in Book IV of the Physics, trying to abolish the void, makes numerous arguments; those that are found beginning with text #64 [214b 10 et sqq.] are drawn from motion. For since he assumes that motion cannot come about in an instant, he tries to demonstrate that, if a void were given, motion in it would happen in an instant: and since assuredly this is impossible, he necessarily concludes that it is impossible for void to exist. Now, since we are dealing with motion, we have decided to inquire whether it is true