relative to the disc by means of the method used in discussing the special theory, and as long as the co-ordinates and times of events have not been defined, we cannot assign an exact meaning to the natural laws in which these occur.
Thus all our previous conclusions based on general relativity would appear to be called in question. In reality we must make a subtle detour in order to be able to apply the postulate of general relativity exactly. I shall prepare the reader for this in the following paragraphs.
[20]The field disappears at the centre of the disc and increases proportionally to the distance from the centre as we proceed outwards.
[21]Throughout this consideration we have to use the Galileian (non-rotating) system
as reference-body, since we may only assume the validity of the results of the special theory of relativity relative to
(relative to