‘Only the hypothesis of the general value of the principle of Relativity in mechanics could admit the Copernican system into physics, since this principle guarantees the independence of all processes on the earth from the progressive motion of the earth. For, if we had to make allowance for this motion, then I should, for instance, have to reckon with the fact that the piece of chalk in my hand possesses the enormous kinetic energy corresponding to a velocity of about 30 km/sec.’