would no longer bisect the angle formed by his own world-line
and the space axis
. The physical significance of this fact was that the velocity of light for the moving observer would be less than for the embankment observer. Now this result contradicted the principle of the invariant velocity of light. If, therefore, we wished to conceive of a graph capable of yielding results in conformity with the principle, we should have to assume that for all observers moving along the embankment, the line
would bisect the angle formed by their respective world-lines and space axes. It followed that the space axis of the moving observer could no longer be Ox but a new line
, such that