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For example, we learn that a body which is in a state of uniform

rectilinear motion with respect to K (in accordance with the law

of Galilei) is executing an accelerated and in general

curvilinear motion with respect to the accelerated reference-body

K′ (chest). This acceleration or curvature corresponds to the

influence on the moving body of the gravitational field

prevailing relatively to K. It is known that a gravitational

field influences the movement of bodies in this way, so that our

consideration supplies us with nothing essentially new.