What is the seat of a movement acting on an object by passing from internal power to actualization? Is it in the motor? How will that which is moved and which suffers be able to receive it? Is it in the movable element? Why does it not remain in the mover? Movement must therefore be considered as inseparable from the mover, although not exclusively; it must pass from the mover into the mobile (element) without ceasing to be connected with the mover, and it must pass from the mover to the moved like a breath (or influx).[426] When the motive power produces locomotion, it gives us an impulse and makes us change place ceaselessly; when it is calorific, it heats; when, meeting matter, it imparts thereto its natural organization, and produces increase; when it removes something from an object, this object decreases because it is capable thereof; last, when it is the generative power which enters into action, generation occurs; but if this generative power be weaker than the destructive power, there occurs destruction, not of what is already produced, but of what was in the process of production. Likewise, convalescence takes place as soon as the force capable of producing health acts and dominates; and sickness occurs, when the opposite power produces a contrary effect. Consequently, movement must be studied not only in the things in which it is produced, but also in those that produce it or transmit it. The property of movement consists therefore in being a movement endowed with some particular quality, or being something definite in a particular thing. MOVEMENT OF DISPLACEMENT IS SINGLE. 24. As to movement of displacement, we may ask if ascending be the opposite of descending, in what the circular movement differs from the rectilinear movement, what difference obtains in throwing an object at the head or at the feet. The difference is not very clear, for in these cases the motive power is the same. Shall we say that there is one power which causes raising, and another that lowers, especially if these movements be natural, and if they be the result of lightness or heaviness? In both cases, there is something in common, namely, direction towards its natural place, so that the difference is derived from exterior circumstances. Indeed, in circular and rectilinear movement, if someone move the same object in turn circularly and in a straight line, what difference is there in the motive power? The difference could be derived only from the figure (or outward appearance) of the movement, unless it should be said that the circular movement is composite, that it is not a veritable movement, and that it does not produce any change by itself. In all of these cases, the movement of displacement is identical, and presents only adventitious differences. EXPLANATION OF COMPOSITION AND DECOMPOSITION.