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These inadequate remarks can give the reader only a vague notion

of the important idea contributed by Minkowski. Without it the

general theory of relativity, of which the fundamental ideas are

developed in the following pages, would perhaps have got no

farther than its long clothes. Minkowski's work is doubtless

difficult of access to anyone inexperienced in mathematics, but

since it is not necessary to have a very exact grasp of this work

in order to understand the fundamental ideas of either the

special or the general theory of relativity, I shall leave it

here at present, and revert to it only towards the end of Part

II.

PART II: THE GENERAL THEORY OF RELATIVITY

XVIII.

SPECIAL AND GENERAL PRINCIPLE OF RELATIVITY

The basal principle, which was the pivot of all our previous

considerations, was the special principle of relativity, i.e. the

principle of the physical relativity of all uniform motion. Let

as once more analyse its meaning carefully.