In his analysis of his new image (Bild) of mechanics Heinrich Hertz (PM 29) distinguished between its physical content and its mathematical form. The physical content was characterized by the assumption that neither force nor potential energy are fundamental quantities of mechanics. When a mechanical system seems to be acted on by forces, it is, according to Hertz, because it is rigidly connected to another system of hidden masses whose fast cyclic motions to a first approximation have the same effect as forces in the traditional Newtonian-Lagrangian image of mechanics. The mathematical form of Hertz's mechanics was characterized by a geometric structure of configuration space that he called the geometry of systems of points.