Inaudi, the French calculator, can look at a blackboard filled with numbers for a few seconds, then turn his back upon them and add the entire amount that he has just seen and memorized. But let the reader understand that Inaudi is peculiarly gifted by nature, while second sight is a trick in which the person on the stage known as the medium is assisted by words, signs, prearranged movements, or articles or figures in rotation, which to the layman have the appearance of being unprepared. At a familiar cue, however, the operator touches articles that have been memorized, a ring, a watch, a scarf-pin, a lady's fan, an opera glass, all in rotation. At a snap of the fingers the medium will know that the articles are to be named in consecutive order, and only after the snap of the fingers or another cue agreed upon. [Illustration: Programme used by Robert Heller in 1851-52, when he was about eighteen years of age. Probably the only programme of this date in existence. Now in the Harry Houdini Collection.] Robert-Houdin presented the trick for the first time at his own theatre, February 12th, 1846. Unquestionably at this time he employed the speaking code, wherein the answer is contained in the question asked of the medium by the performer. As he describes scene after scene in which he and his son participated, it is almost possible for a conjurer or any one interested in magic to follow his code. Apparently the amusement-loving public became familiar with his speaking code, for three years later, according to the illustrated appendix of the French edition of his "Memoirs," he adopted a code of signals, which he states was especially arranged to confuse those whom he terms his "fearless discoverers."