Compendium of All Natural Science

...and other motions, which we have noted are called reflected by philosophers: for since these begin from that place where they had previously arrived, they are most rightly considered reflected. Wherefore, since some rest intervenes, they cannot be continuous. Moreover, every motion is compared to a motion of the same genus: so that a straight motion is compared to a straight one, and that which is circular to that which is circular, being entirely equal or unequal; likewise faster and slower, and many other such kinds of comparison.

On the velocity of motion, which is derived from that proportion which exists between the proportions of the moving forces. 19.

Now, the velocity of motion is derived from that proportion which exists between the proportions of the moving things to the resisting impediments. For if Sofias can move a third part, but moves a sixth, the proportion of the mover to the moved will be double. Again, if Davus can move a fourth part, but moves an ounce, the proportion of the mover to the moved will be triple. Indeed, as the proportion is drawn from the double to the triple, such also will be the proportion of the velocity of each mover. Wherefore we shall conclude that the proportion is hemiolic—that is, sesquialterate—which exists between that which moves an ounce although it is capable of a fourth, and that which moves a sixth although it is capable of a third. Wherefore, in this way, that which is less...