At ten o'clock, in fact, one of the neighbours living nearest to the lodge, from whose house my uncle or Bérangère had been in the habit of telephoning, sent word to say that he was connected with Paris and that I was asked to come to the telephone without losing a minute. I went round in a very bad temper. I was worn out with fatigue. It was raining cats and dogs; and the night was so dark that I knocked against the trees and houses as I walked. The moment I arrived, I took up the receiver. Some one at the other end addressed me in a trembling voice: "M. Beaugrand . . . M. Beaugrand . . . Excuse me . . . I have discovered . . ." I did not understand at first and asked who was speaking. "My name will convey nothing to you," was the answer. "Benjamin Prévotelle. I'm not a person of any particular importance. I am an engineer by profession; I left the Central School two years ago." I interrupted him: "One moment, please, one moment. . . . Hullo! . . . Are you there? . . . Benjamin Prévotelle? But I know your name! . . . Yes, I remember, I've seen it in my uncle's papers." "Do you mean that? You've seen my name in Noël Dorgeroux's papers?" "Yes, in the middle of a paper, without comment of any kind." The speaker's excitement increased: "Oh," he said, "can it be possible? If Noël Dorgeroux made a note of my name, it proves that he read a pamphlet of mine, a year ago, and that he believed in the explanation of which I am beginning to catch a glimpse to-day." "What explanation?" I asked, somewhat impatiently. "You'll understand, monsieur, you'll understand when you read my report." "Your report?" "A report which I am writing now, to-night. . . . Listen: I was present at both the exhibitions in the Yard and I have discovered. . . ." "Discovered what, hang it all?" "The problem, monsieur, the solution of the problem." "What!" I exclaimed. "You've discovered it?" "Yes, monsieur. I may tell you it's a very simple problem, so simple that I am anxious to be first in the field. Imagine, if any one else were to publish the truth before me! So I rang up Meudon on the chance of getting you called to the telephone. . . . Oh, do listen to me, monsieur: you must believe me and help me. . . ." "Of course, of course," I replied, "but I don't quite see . . ." "Yes, yes," Benjamin Prévotelle implored, appealing to me, clinging to me, so to speak, in a despairing tone of voice. "You can do a great deal. I only want a few particulars. . . ." I confess that Benjamin Prévotelle's statements left me a little doubtful. However, I answered: "If a few particulars can be of any use to you . . ." "Perhaps one alone will do," he said. "It's this. The wall with the screen was entirely rebuilt by your uncle, Noël Dorgeroux, was it not?" "Yes." "And this wall, as you have said and as every one had observed, forms a given angle with its lower part." "Yes."