"Moreover, it is a matter of common experience that a madman always understands everything. But this man wanted to understand. I begged him to repeat the story. He said nothing. Twice I reiterated the request and still he said nothing. I was about to lose patience, when, grasping the fact that I had asked him something, he told me that now and then he was deaf for a few minutes. "Since he had recovered his hearing, we returned to the problem of the express. He assured me that he would rather die ten times in the depths of the Catacombs than come out of them once without knowing what had become of this express. 'I do not wish,' he added, 'to lose the most precious thing in the world: my Reason.' "'And when did this happen?' said I. 'For, as a matter of fact, I have heard nothing of the disappearance of an express; and it ought to be generally known.' "'It must be known by now,' he, said in a very melancholy tone. 'It only happened a few hours before our fall into the Catacombs.' "I examined the paper once more for quite five minutes. I reflected deeply, asked for certain complementary details, and then burst out laughing: though in truth it was not a laughable matter, for the catastrophe was truly appalling. What made me laugh was the seeming difficulty of the problem and the delight of having solved it in five minutes. "'You believe yourself a rational human being,' I cried, 'because you have Reason! But you're exactly like ninety-nine people out of a hundred, you don't know how to make use of it. You talk of Reason; _but what use is Reason in a brain which does not know by which end to take hold of it_? It's a wonderful instrument in the hands of a doll! Don't turn away your head in that sulky way, M. Longuet. I tell you: _you don't know by which end to take hold of your Reason!_ Come, M. Longuet: let us reason with this paper in our hands.' "He tried, the duffer! He said: 'There were five men at A, and five men at B. The five men at B saw the train pass; the five men at A did not see it. I--I was at K; and I am sure that it did not pass at K... consequently...' "'Consequently?... Consequently, there's no longer any express? Consequently your express has vanished--melted--flown away? Hey, presto: vanish express! _You think perhaps that the express is in the English Channel!_ You see clearly, M. Longuet, that if you have Reason, you don't know how to use it. Allow me to tell you _that you took hold of your Reason by the wrong end!_ The wrong end is that which begins by saying, 'We did not see the express,' and which ends by saying, 'Then there is no longer any express!' But I am going _to show you how to take hold of your Reason by the right end_. It is this: the truth is that the express exists, and that it exists between the points B, where it was seen to pass, A, where it was not seen to pass, and I, where it could not pass. Since we are in a plain, your express is between A, B and I. That is certain...' "'But!'