brought Niepce and Daguerre together, when they entered into partnership to prosecute the subject in common. For a long time they appear to have used the resinous surfaces only, when the contrast between the resin and the metal plates not being sufficiently great to give a good picture, endeavors were made to blacken that part of the plate from which the resin was removed in the process of _heliography_ (sun-drawing), as it was most happily called. Amongst other materials, iodine was employed; and Daguerre certainly was the first to notice the property possessed by the iodine coating of changing under the influence of the sun's rays. The following letter from Niepce to Daguerre is on this subject: "81, LOUP DE VARENNES, June 23, 1831. "_Sir, and dear Partner_: I had long expected to hear from you with too much impatience not to receive and read with the greatest pleasure your letters of the tenth and twenty-first of last May. I shall confine myself in this reply to yours of the twenty-first, because, having been engaged ever since it reached me in your experiments on iodine, I hasten to communicate to you the results which I have obtained. I had given my attention to similar researches previous to our connection, but without hope of success, from the impossibility, or nearly so, in my opinion, of fixing in any durable manner the images received on iodine, even supposing the difficulty surmounted of replacing the lights and shadows in their natural order. My results in this respect have been entirely similar to those which the oxide of silver gave me; and promptitude of operation was the sole advantage which these substances appeared to offer. Nevertheless, last year, after you left this, I subjected iodine to new trials, but by a different mode of application. I informed you of the results, and your answer, not at all encouraging, decided me to carry these experiments no farther. It appears that you have since viewed the question under a less desperate aspect, and I do not hesitate to reply to the appeal which you have made. "J. N. NIEPCE."