  However, Einstein also tried to extend and generalize the special theory of relativity by incorporating version (2) of Mach’s Principle into the general theory of relativity. Einstein was deeply influenced by Mach’s empiricist programme and accepted Mach’s insistence on the primacy of observable facts of experience: only observable facts of experience may be invoked to account for the phenomena of motion. As a consequence, Einstein restricted the concept of relative motions to relative motions between bodies. Newton thought that the plane of Foucault’s pendulum remains aligned with respect to absolute space. Since the fixed stars are at rest with respect to absolute space the plane of Foucault’s pendulum remains aligned to them as well, and rotates relative to the earth. But according to Einstein, Newton’s intermediary notion of absolute space is as questionable as it is unnecessary in explaining the behaviour of Foucault’s pendulum. Not absolute space, but the actually existing masses of the fixed stars of the whole cosmos guide the plane of Foucault’s pendulum. 