24. With regard to locomotion: if ascending is to be held contrary to descending, and circular motion different [in kind] from motion in a straight line, we may ask how this difference is to be defined- the difference, for example, between throwing over the head and under the feet. The driving power is one- though indeed it might be maintained that the upward drive is different from the downward, and the downward passage of a different character from the upward, especially if it be a natural…