The actio in distans can also be proved from the very nature of material activity. It is generally admitted that the active power of matter is either attractive or repulsive; for all men of science agree that the movements of the material world are brought about by attractions and repulsions. Now, attraction and repulsion do not imply a material contact between the agent and the patient, but, on the contrary, exclude it; and therefore all the movements of the material world are due to actions at a distance. That attraction excludes material contact is quite evident, for attraction produces movement by causing the approach of one body to another; and it is evident that no approach will be possible if the bodies are already in immediate contact. It is therefore an essential condition for the possibility of attraction that the agent be not in immediate contact with the patient. And as for repulsion, it is known that it serves to keep the molecules of a body distant from one another, and consequently it is exercised at molecular distances. This is especially evident in the case of elastic fluids. For repulsion obtains among the molecules of such fluids, whether the said molecules be pressed nearer or let further apart. And therefore repulsion, too, is exercised without material contact.
Some modern physicists try to do away with repulsion, and explain the pressure exercised by a gas against the vessel in which it is confined by saying that the gaseous molecules are continually flying about in all directions, and continually impinging on the interior surface of the recipient, where their excursions are intercepted, and that this continuous series of impacts constitutes what we call the pressure of the gas on the vessel.
But this new theory cannot bear one moment's examination. It is wholly gratuitous; it disregards mechanical principles by admitting that the movement of the molecules can go on unabated in spite of repeated impacts, and it assumes that the momentum of a moving molecule is its active power; which is utterly false, as we will show later.
Other physicists have tried to get rid of attraction, also, by assuming that those effects which we ascribe to attraction are to be attributed to ethereal pressure. This hypothesis has no better foundation than the preceding one, and is equally untenable for many reasons which we shall explain hereafter.
The actio in distans can also be directly proved by the consideration of statical forces. We know that the action which tends to communicate movement in a given direction cannot be frustrated or neutralized, except by an action of the same intensity applied in an opposite direction. It is evident, on the other hand, that, if the first requires an immediate contact of matter with matter, the second also must be subject to the same condition. Now, this latter is altogether independent of such a condition. Accordingly, the former also—that is, the action which tends to communicate the movement—is independent of a true material contact.
The minor proposition of this syllogism may be proved as follows: Let a small cube of hard steel be placed on a smooth, horizontal plate of cast-iron lying on a table. The cube will remain at rest on the plate, notwithstanding the action of gravity upon it, because, while the cube tends to fall and presses the plate, the action of the plate frustrates that tendency, and keeps the equilibrium. Now, the cube and the plate do not immediately touch one another with their matter; for we know that they can be brought nearer than they are. We may place, for instance, a second cube on the top of the first, and thus increase the pressure on the plate, and cause the plate itself to react with an increased intensity. But it is obvious that neither of the two actions can become intenser, unless the cube is brought nearer to the plate; for the resistance of the plate cannot be modified, unless some of the previous conditions be altered; and since the two surfaces have remained the same, no other condition can be conceived to be changed except their relative distance. It is therefore a change, and in fact a diminution, of the distance between the cube and the plate that entails the change of the action. Whence we see that, even in the case of the so-called physical contact, bodies do not touch one another with their matter. This shows that physical contact does not exclude distance; and therefore, when we say that two bodies touch one another, the fact we express is that the two bodies are so near to one another that they cannot approach nearer [pg 587]without their molecular arrangement being disturbed by their mutual actions. Therefore the hypothesis that a true material contact of matter with matter is needed for causing or for hindering movement is irreconcilable with fact.
As a further development of this proof, we may add that one of the necessary conditions for the equilibrium of the cube on the plate is, that the action of the plate have a direction opposite to the action of the cube. Now, no direction whatever can be conceived but between two distinct, and therefore distant, points. Accordingly, there cannot be the least doubt that all the points belonging to the surface of the plate are really distant from those of the neighboring surface of the cube. Whence we conclude again that their mutual action is exercised at a distance.
Other proofs of the same truth might be drawn, if necessary, from other considerations. Faraday, from the phenomena of electric conduction, was led to the conclusion that each atom of matter, though occupying a mere point in space, has a sphere of action extending throughout the whole solar system.[134] Boscovich,[135] from the law of continuity, demonstrates that movement is not communicated through material contact. And mechanical writers generally consider all dynamical forces—that is, all accelerating or retarding actions—as functions of distances; which shows that all motive actions depend on distance, not only for their direction, but also for their intensity. We have no need of developing these proofs, as we think that the preceding arguments are abundantly sufficient to convince all intelligent readers of the truth of our conclusion, viz.:
1. That distance is a necessary condition of the action of matter upon matter;
2. That the contact between the agent and the object acted on is not material, but virtual, inasmuch as it is by its active power (virtus), and not by its matter, that the agent reaches the matter of the object acted upon;