From this and other letters it is evident that Niepce had used iodine, and abandoned it on account of the difficulty of reversing the lights and shadows. Daguerre employed it also, and, as it appears, with far more promise of success than any obtained by M. Niepce. On the fifth of July, 1833, Niepce died; in 1837 Daguerre and Isodore Niepce, the son and heir of Nicephore Niepce, entered into a definite agreement; and in a letter written on the first November, 1837, to Daguerre, Isodore Niepce says, "What a difference, also, between the method which you employ and the one by which I toil on! While I require almost a whole day to make one design, you ask only four minutes! What an enormous advantage! It is so great, indeed, that no person, knowing both methods, would employ the old one." From this time it is established, that although both Niepce and Daguerre used iodine, the latter alone employed it with any degree of success, and the discovery of the use of mercurial vapor to produce the positive image clearly belongs to Daguerre. In January, 1839, the Daguerreotype pictures were first shown to the scientific and artistic public of Paris. The sensation they created was great, and the highest hopes of its utility were entertained. On the 15th June, M. Duchatel, Minister of the Interior, presented a bill to the Chamber of Deputies relative to the purchase of the process of M. Daguerre for fixing the images of the camera. A commission appointed by the Chamber, consisting of Arago, Etienne, Carl, Vatout, de Beaumont, Toursorer, Delessert (François), Combarel de Leyval, and Vitet, made their report on the third of July, and a special commission was appointed by the Chamber of Peers, composed of the following peers: Barons Athalin, Besson, Gay Lussac, the Marquis de Laplace, Vicomte Simeon, Baron Thenard, and the Comte de Noe, who reported favorably on the thirtieth July, 1839, and recommended unanimously that the "bill be adopted simply and without alteration." On the nineteenth of August the secret was for the first time publicly announced in the Institute by M. Arago, the English patent having been completed a few days before, in open defiance and contradiction of the statement of M. Duchatel to the Chamber of Deputies, who used these words, "Unfortunately for the authors of this beautiful discovery, it is impossible for them to bring their labor into the market, and thus indemnify themselves for the sacrifices incurred by so many attempts so long fruitless. This invention does not admit of being secured by patent." In conclusion, the Minister of the Interior said, "You will concur in a sentiment which has already awakened universal sympathy; you will never suffer us to leave to foreign nations the glory of endowing the world of science and of art with one of the most wonderful discoveries that honor our native land." Daguerre never did much towards the improvement of his process.