To replace the concept of force, he proposed that the acceleration of visible masses are to be accounted for, not by force, but by geometric constraints on the visible masses, and their geometric linkages to invisible masses. In this, he understood himself as continuing the tradition of Cartesian mechanical philosophy, such as Boltzmann 's explaining of heat by atomic motion, and Maxwell's explaining of electromagnetism by ether motion. Even though both atoms and the ether were not observable except via their effects, they were successful in explaining apparently non-mechanical phenomena mechanically. In trying to explain away "mechanical force", Hertz was "mechanizing classical mechanics".