On page 17 of the American edition Robert-Houdin starts his dramatic tale of inventing a detector lock by which he protected a rich neighbor, M. de l'Escalopier, from robbery, and incidentally in return secured funds with which to open his theatre in the Palais Royal. In his "Mémoirs" Robert-Houdin states that the opening of the theatre was made possible by the invention of the writing and drawing automaton whose history has been traced in chapter III. The reader can choose between the two stories. One is as plausible as the other. But to return to the detector lock. Count or M. De l'Escalopier having complained grievously to his humble neighbor, the watchmaker Robert-Houdin, that he and his family were being robbed, begged that the latter suggest some means of catching the thief. Robert-Houdin then recalled a childish device by which he had caught his school-fellows in the act of pilfering his desk, etc., and he proposed to the Count that the same device, elaborated to meet the strength of a full-grown man, be attached to his wealthy patron's desk. As first planned, the detector lock was to shoot off a pistol on being tampered with, and then brand the hand of the thief with nitrate of silver. Count de l'Escalopier objected to branding a man for life, so Robert-Houdin substituted for the nitrate of silver a sort of cat's claw which would clamp down on the robber's hand and draw blood. The Count deposited ten thousand francs in his desk and caught the robber, his confidential servant, red-handed. The ten thousand francs he presented to Robert-Houdin as a reward for stopping the thefts. A charming tale this makes, but, unfortunately for Robert-Houdin's claims to originality, the detector lock was not a novelty in his day. The lock which would first alarm the household by setting off a pistol and then brand the thief's hand, is described by the Marquis of Worcester in his book "Centurie of Inventions." As locks and locksmithing form my hobby, while in England I purchased the entire set of patent-books, to add to a collection of locks and fastenings from every known country of the world. In the introduction of the first book of patents for inventions relating to locks, latches, bolts, etc., from A.D. 1774 to 1866, the following quotation will be found: "The Marquis of Worcester in his 'Centurie of Inventions' thus describes the first detector lock invented, A.D. 1640, by some mechanical genius of that day: 'This lock is so constructed that, if a stranger attempts to open it, it catches his hand as a trap catches a fox, though not as far as maiming him for life, yet so far marketh him that if suspected he might easily be detected.'"