"'Hush! Be quiet! And since we are in a plain, and in that plain there is an immense mass of loose sand, the only place in which the train could have disappeared is in that mass of sand: _that is the eternal truth!_'... "'I swear it didn't! I was at K waiting for the express; and I did not quit the line H I.' "'By the immortal Masterpieces of the Italian Renaissance I command you not to let go of the right end of your Reason which I have put into your hand. We are discussing at this moment what _is_; we are not yet at the _how_. It is owing to the fact that you began with the _how_ that you have not been able to reach what _is_. _The express is in I, since it cannot be anywhere else._ I am sure that the five men could not have seen it pass B, as they assert, unless it had passed. I am as certain that five men could not have been unable to see it at A if it had passed A; and since the line A B was examined and found not to contain the express, it must be that it turned off up the line H I. There we are, then, with the train on the line H I.' "'But I was there too,' cried Theophrastus, 'and I swear to you _that it wasn't_!' "'Dear! Dear! Do hold on to the right end of your Reason! You were at K; the express passed K; _it must pass K_; _it must go and plunge into I, since it cannot be anywhere else_. By a _necessary_ chance, while the beginning of the train is engulfed in the mass of sand (I take it for granted that the line H I is too short for the engine-driver, having perceived the error of direction half-way up it, to have had the time to ward off the catastrophe), the couplings of the last carriage broke, and the carriage and the guard's-van began to descend the line which was on a slope since it went to this mass of sand. There, after having gone down the line to H and back up it to K, you saw the carriage and Signor Petito at the window. (Probably Signor Petito opened the window with the intention of jumping out, at the moment he grasped the imminent catastrophe, and as it happened the shock of it shut his head in the window.)' "'That I understand; but what I don't understand...'