It is the easily bounded, in proportion as it is easily bounded, which is easily divided; and air is more so than water, water than earth.
Further, the smaller the quantity in each kind, the more easily it is divided and disrupted.Thus the reason why broad things keep their place is because they cover so wide a surface and the greater quantity is less easily disrupted.Bodies of the opposite shape sink down because they occupy so little of the surface, which is therefore easily parted.And these considerations apply with far greater force to air, since it is so much more easily divided than water.But since there are two factors, the force responsible for the downward motion of the heavy body and the disruption-resisting force of the continuous surface, there must be some ratio between the two.For in proportion as the force applied by the heavy thing towards disruption and division exceeds that which resides in the continuum, the quicker will it force its way down; only if the force of the heavy thing is the weaker, will it ride upon the surface.
We have now finished our examination of the heavy and the light and of the phenomena connected with them.
THE END