It will probably be felt that this result is due to our having, somewhat unjustifiably and inconsistently, localized on the train the relative motion between train and track. But if we think of the track as sliding back under the train in the direction opposite to the arrow, and carrying with it the points $A$ and $B$; and if we remember that this in no way affects $M$'s observed velocity of light or the distances $AM$ and $BM$ as he observes them: we can still accept his claim that the flashes were simultaneous. Then we have again the same situation: when the flashes from $A$ and from $B$ reach $M$ at the same moment, in his new position a trifle to the left of his initial position of the diagram, the flash from $A$ has not yet reached $M'$ in his original position while that from $B$ has passed him. Regardless of what assumption we make concerning the motion between train-system and track-system, or more elegantly regardless of what coordinate system we use to define that motion, the event at $B$ precedes that at $A$ in the observation of $M'$. If we introduce a second train moving on the other track in the opposite direction, the observer on it will of course find that the flash at $A$ precedes that at $B$--a disagreement not merely as to simultaneity but actually as to the order of two events! If we conceive the lightning as striking at the points $A'$ and $B'$ on the train, these points travel with $M'$ instead of with $M$; they are fixed to his coordinate system instead of to the other. If you carry out the argument now, you will find that when the flashes are simultaneous to $M'$, the one at $A$ precedes that at $B$ in $M$'s observation. A large number of experiments more or less similar in outline to this one can be set up to demonstrate the consequences, with regard to measured values of time and space, of relative motion between two observers. I do not believe that a multiplicity of such demonstrations contributes to the intelligibility of the subject, and it is for this reason that I have cut loose from immediate dependence upon the essayists in this part of the discussion, concentrating upon the single experiment to which Einstein himself gives the place of importance. WHO IS RIGHT?