The fundamental distinction between space and time, i.e. between rects and point-tracks, has failed to find any expression in the formulae for measurement relations. Accordingly with this type of kinematics, it would be natural to suppose that the distinction does not exist and that every rect was a point-track and every point-track a rect. This conception is logically possible but does not appear to correspond to the properties of the external world of events as we know it. Furthermore the electromagnetic equations lose their invariant property.
Altogether there appear to be good reasons for putting aside the elliptic type of kinematics as inapplicable to nature.
52.8 In the parabolic type of kinematics we put
Hence
Then from (ii) of [51.1] and (ii) of [50.3] and (iii) of [50.1]