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Analogously, I seek in vain for a real something in classical

mechanics (or in the special theory of relativity) to which I can

attribute the different behaviour of bodies considered with

respect to the reference systems K and K′.[15] Newton saw this

objection and attempted to invalidate it, but without success.

But E. Mach recognised it most clearly of all, and because of

this objection he claimed that mechanics must be placed on a new

basis. It can only be got rid of by means of a physics which is

conformable to the general principle of relativity, since the

equations of such a theory hold for every body of reference,

whatever may be its state of motion.

[15] The objection is of importance more especially when the

state of motion of the reference-body is of such a nature that it

does not require any external agency for its maintenance, e.g. in

the case when the reference-body is rotating uniformly.

XXII.

A FEW INFERENCES FROM THE GENERAL PRINCIPLE OF RELATIVITY