INTRODUCTION TO SOCIOLOGY 487
far as possible from foreign influences ; and, being unable to suppress movement entirely, they at least maintained the unity of its direction, knowing very well, in general, that when a move- ment is arrested by an obstacle the force manifests itself by a pressure or a traction upon the obstacle.
In reality, up to the eighteenth century political science was based mainly upon mechanics, and through mechanics was united to geometry and arithmetic. In fact, forces may always be expressed in units of weight which in turn are convertible into units of length. The law of Newton was one application of this valuation which was extended to political science : action is equal and opposite to reaction, the body of impact is itself always the object of an equal but contrary pressure exercised by the body of resistance.
In like manner the mechanical law of independence of move- ments dominated politics; whatever the development of the state might be, the relations of the citizens to each other, the social system, need not thereby be altered. From the simplest point of view, this law expressed the general fact that a uniform, rec- tilinear movement, exactly common to all the bodies of any system, does not modify the particular movements of those dif- ferent bodies with respect to each other; these movements con- tinue to take place just as if the whole of the system were immobile. Thus, in the case of a moving ship, whatever may be the swiftness and the direction of its motion, the relative move- ments of the objects and the persons on board take place as if the ship were immobile, although to outside observers these movements form part of the whole movement. It appeared to be the same in the case of the voyagers upon the ship of state.
Moreover, it was an eminently scientific point of view to extend to societies the mechanical principle that forces are always proportional to the accelerations of motion that they produce.
Social statics was, then, a mechanical statics. Like the lat- ter, it treated of the conditions of equilibrium of a system; in it the element of time was not considered. A phenomenon was considered as fixed, the variations which the forces of the sys-
