A material agent, when pulling another body by its own motive force, must necessarily be agitated in some way and move. If indeed the agent is supposed to be absolutely inert and stable, how will it agitate another contiguous body and displace it? Actually, when the agent moves from one place to another, I understand that a body connected to it must be expelled from its position. Otherwise the agent body would not move. This is obvious since two bodies cannot interpenetrate each other. Consequently, if the object body is fluid, it must at least be displaced sideways to let the impelling body free passage. If it is hard and consistent, the impelling body will move it away as a whole by expelling it. If the ambient body does neither oppose nor impede the forwards movement of the impelling body but adheres to it behind, if it is attached by a rope or a hook or some similar curved device, it may happen that the attached following body moves with the agent. This is logical. The curved part of the pulling instrument which is impelled forwards by the agent, is impelled forwards as a result of the impenetrability and the body tied behind is moved because of the hardness and solidity of this curved part. If the rope or the hook or the other curved instrument is removed, I do not see and do not understand how the anterior body while moving must pull with it the posterior body which is not attached to it by any tie or glue.

But there are philosophers who say: it is equally easy to conceive that a tensed body while retracting itself pulls with it another contiguous body as a compressed body displaces from itself another body. There is no need of a rope to this end since, according to the institution of Nature, all bodies are parts of the universe and parts which compose a whole must be united. Otherwise they would not be parts if they could be separate. Therefore, one body adheres to the other.

The necessity of this operation appears from the fact that a body cannot be moved to occupy the position of another body without expelling the latter since two bodies cannot be set in the same place. That a body while moving away from the position of another body must pull with itself by adherence a contiguous body behind from the contact of which it attempts to recede and to which it is not tied by some glue, a rope or another bound, not only is asserted gratuitously but seems to be absolutely impossible and is beyond any understanding. When he says that the institution of Nature is that the worldly bodies are parts of the universe, I admit it. But I deny that the parts which compose a whole must be united and that otherwise they would not be parts if they could separate. Indeed, the parts of an army are distinct and, however, they compose the army. Several separate small lines could also compose the whole length of a palm as if they were united, straight or twisted. I notice that the word conjunction does not mean absolutely firm union and linkage, but simple contact of the parts such as that which connects a heap of sand and of grains of wheat. Water indeed attracted by adjacent air or by a piston is neither bound nor united to them but adheres by simple contact only. Anybody who wants to speak seriously and sincerely will understand that it is impossible that subsequent grains of wheat be pulled by precedent ones and follow the movement of the latter by the force of simple contact without any tie or glue. Unquestionably, such movement could be carried out if the subsequent grains were impelled by some motive force. Some move spontaneously either by their own will, such are the animals, or by blind necessity, such are the heavy bodies. But all this does not occur in our instance.

But not to dog further words uttered gratuitously, I notice that the opponents will never prove that there is in nature an attractive force or quality unless they show by the evidence of the senses or by a demonstration that bodies which seem to be attracted are not moved spontaneously by an intrinsic force and are not impelled by an external body. Since they will never prove this, they cannot claim that there is attraction in nature. Therefore, it is permitted to deny their assertion.

On the contrary, if we show that some bodies among those which seem to be attracted by a natural force, move spontaneously and arrive at other bodies and the others actually are impelled by an external force, the attractive force and quality will be knocked down from the nature of things.

Firstly, as far as iron and magnet are concerned, I showed (Book on the Force of Percussion) that these two bodies are moved towards each other spontaneously by a natural force as heavy bodies are brought spontaneously to the earth. The cause of the attraction of electric bodies by others has been explained. Experience indeed shows that, electric bodies, unless being warmed by friction with some cloth, do not attract small and light straws in their vicinity. These are set in a kind of atmosphere made of smoky and warm exhalations surrounding the electric body. The mass made of these vapours and the straws becomes lighter than the contiguous air, more remote. This expresses and constricts this smoky mass from everywhere towards the solid electric body and thus carries with it the straws.

Fluid and soft bodies are brought to the pumps, the water organ of Ctesibius and in medical cupping-glasses not spontaneously but impelled by an external force. This is nothing else than the simple gravity of the ocean of air surrounding the terrestrial globe and which compresses water and all subjacent soft bodies, as appears from the theory of hydrostatics presented above. Therefore, when the piston is raised in a pump or when internal air is rarefied in a cupping-glass, the subjacent fluid and soft part less compressed by the ambient air must be expelled upwards by the more compressed part. It would thus be stupid to resort to an attractive force and quality of the piston or the cupping-glass to raise the water since there is a true and necessary cause of this effect. This cause is the column of air compressing the subjacent water. The water is introduced and expressed into the pump or the cupping-glass by this impulsive force.

But this will be explained more clearly in due place. Meanwhile, I will tackle the fairly plausible objection which is usually raised against this theory. People say indeed that when cupping-glasses attract flesh or the pulp of a finger is introduced into a pump, this part of flesh or of the finger introduced into the cupping-glass or the pump hurts. But no pain or harm is perceived in the remainder of the animal body nor in the proximal part of the finger. Actually, pain cannot be produced by nothing and, inversely, an active cause achieving compression should entail pain. Consequently, pain should be perceived not in the pulp of the finger but rather at the opposite side, in the nail. Similarly, pain should not be felt in the back where the cupping-glasses are applied but rather in the chest where compression and squeezing by ambient air occur. The pulp or flesh introduced in the cupping-glass or in the pump should perceive no pain since the cause which impels and compresses the flesh by its violence is not there.

To refute this objection some points which have been mentioned previously must be repeated. When it was asked why divers in deep sea do not perceive the considerable gravity of the incumbent water, we said that this results from the fact that water compresses the immersed body of the animal from everywhere, from above, from below and from the sides, with an equal effort. We showed that an impulsion and compression carried out in one particular place can achieve dislocation, rupture and bruising. On the other hand, if the same compressive virtue is multiplied so as to impel and compress the body of the animal from everywhere, we showed that, not only the harm and pain are not increased, but on the contrary no dislocation nor bruising and thus no pain can be generated. This appears most obvious from what was demonstrated above. Moreover, we said that, although considerable dislocation and solution of continuity do not result from this overall compression by the fluid, some constriction of the whole body cannot be denied. One must feel this in the depths of the ocean because of its unusual character. But in the air, an animal must in no way perceive any pain from its universal compression and constriction because it is used to it. Since their birth the animals are always surrounded and constricted by this air coating. Thus, compression by air does not produce any change in the animal and, therefore, this thinks he is not constricted or compressed by any ambient force. Consequently, the flesh, vessels and viscera undergo some constriction from the said compressive force but they cannot perceive it at all. Even intermittent constrictions, like those due to our clothes, usually are not painful because we are used to.