We supposed with Archimedes that water and all the other fluid bodies surrounding the earth exert a compression towards the centre of the earth by the force of their own gravity. Consequently, they are arranged spherically about the centre of the earth. Moreover, we supposed, also with Archimedes, that the less compressed parts of the fluid are expelled and moved upwards by its more compressed and heavier parts. From this hypothesis, it is deduced that every fluid such as water has a gravity and exerts it even in its proper place and natural location, i.e. water itself, while immobile in all the water, exerts its gravity by compressing the underlying bodies.

But this is denied by many people who think that Archimedes thought the opposite. Some peripatetics also deny it. They think that it is not always true that the upper parts of a heavy body compress and exert a force on the lower and adjacent parts unless the lowest parts are light absolutely or relatively and, hence, give way. For example, put over water or over air, they exert their force and action of gravity and compression but it is different for water put on the earth, or air incumbent over water, or air present above air, or water put over water. They attempt at confirming this proposition by the following argument. Since Nature is the cause and principle of movement and does not act in vain but to a certain end and to the good, it unquestionably ordered the movement of natural bodies to a certain end and to the good, i.e. to the conservation. The action or perfection which heavy and light bodies desire and attempt at acquiring when moving is their displacement to and their presence in their proper natural places, that of the heavy bodies below, that of the light ones above. Consequently, when they have been brought to their due natural places, movement stops completely, according to the desire of Nature and the achievement of the end, since, as Aristotle said, Nature does not move a body in order to move it, i.e. to agitate it perpetually and ad infinitum but only to bring it to its aim and goal so that it can be immobile there. Actually, the faculties or virtues which move the sublunary bodies to their proper places are nothing else than gravity or lightness. Consequently, these faculties are programmed to lead the elementary bodies to their proper places so that they are immobile there. They cannot be of any use later if, after having carried out the movement, they would disturb and confuse the natural position of these bodies in their places. There is indeed agreement that the elements do not try to leave their proper places and, therefore, lack this natural stimulus or principle of movement which impelled them previously to arrive at their natural places. From this it is deduced that no element in its proper place has gravity or lightness. Water put in water remains in its proper and natural region. It is the same for air in air. Thus none of these elements has or exerts gravity in its place. Firstly, as far as Archimedes is concerned, opponents seem in no way to have understood this great man, as plainly appears from his words. To the peripatetics it is enough to say that, not only no positive lightness is to be shown in nature but, moreover, I proved that it is false that, after the normal bodies have arrived to their places and are immobile there, gravity has no use unless to disturb the famous order of the Universe. On the contrary, I will attempt to convince that bodies exert gravity precisely when they are quiescent in their places and, even more, that the cause why they are quiescent in their places is that they exert their weight. But, at first, the action of gravity must be considered and what a weight does above all when compressing. The action and compression of a heavy body of course is not a displacement, for example that of an iron ball while descending towards the earth. Nor is it the simple contact of the ball with the surface of the underlying earth. It is the force and energy which impels the ball downwards and compresses it, as with a wine press, on the earth. A weight hanging from a balance, although it seems immobile, exerts a compressive action of as much energy as is its gravity. We understand that easily. Imagine two men equally healthy and strong who push each other with all their forces. It is obvious here that in the presence of opposite forces equal to each other so that none prevails over the other, none of the wrestlers will be displaced. Each of them remains immobile although exerting all his force and his own faculty in pushing and repelling his opponent. Similarly, when somebody pushes violently a huge column, although he is not able to knock it down or move it so as to result in a displacement of the pushing man or of the column, nevertheless an impulsive movement of the muscles and limbs of the pushing man cannot be denied. Nor can be denied a small and imperceptible bending of the column which, like a bow or a spring, resists the impulse and bending with an equal force. Similarly, when an iron ball rests on a support or a glass sheet, it must be conceded that there is some squeezing of the parts of the compressing iron and of the compressed glass. Their pores are somewhat constricted. In the nature of things (as shown in Chap. 26 of On the Force of Percussion), composite bodies cannot be found so hard that they can resist the compression of any body. The mentioned compression of the glass by a heavy weight occurs. This appears from the fact that, by increasing more and more the compressing weight, finally the support of glass breaks and is squashed as if it was disrupted by a hammer blow. If this was not true, i.e. if the support of glass was not squeezed and compressed by a weight however multiplied and increased, the smallest support of glass would tolerate the compressive force of the weight of a mountain however big, which unquestionably does not occur.

This being said, nobody will deny that, if the weight is doubled or if one is superimposed on the other, the glass support is compressed and squeezed with a double force and vigour. Therefore, the pores are much more diminished by the double impulse since a heavy mass cannot be conceived being increased and multiplied without multiplication of the weight and thus of the compressive force and energy towards the centre of the earth so that the solid and consistent parts are compressed and squeezed much more.

But if this occurs in the hardest bodies, it can certainly not be denied in fluid bodies which are not less heavy and compress the bottom of the vessel in which they are contained with as much force as is the energy of their weight. If the mass of fluid is multiplied by hundred and thousand, the bottom of the vessel is compressed by a force hundred and thousand times greater. Although there is no progressive movement, a tonic movement is never absent, not more than constriction of the pores of the bottom of the vessel and compression of the pores of the fluid if perhaps there are pores. As the fluid weighs and constricts the pores of the bottom of the vessel because of its weight and gravity, there is no reason for the lowest subjacent layers of the fluid which are close to the bottom of the vessel not to be compressed by its weight. The upper parts of the fluid cannot compress the bottom of the vessel without impelling and constricting the lowest layer of this fluid since an action cannot occur at a distance but only by contact impelling the adjacent subjacent parts, layer after layer until they compress the bottom.