Mr. Biot, in 1840, speaking of Mr. Fox Talbot's beautiful calotype pictures, considers as an illusion "the hope to reconcile, not only the intensity but the tints of the chemical impressions produced by radiations, with the colors of the object from which these radiations emanated." It is true that three years have passed away, and we have not yet produced colored images; yet I am not inclined to consider the hope as entirely illusive. It must be remembered that the color of bodies depends entirely upon the arrangement of their molecules. We have numerous very beautiful experiments in proof of this. The bi-niodide of mercury is a fine scarlet when precipitated. If this precipitate is heated between plates of glass, it is converted into crystals of a fine sulphur yellow, which remain of that color if undisturbed, but which becomes very speedily scarlet if touched with any pointed instrument. This very curious optical phenomena has been investigated by Mr. Talbot and by Mr. Warrington. Perfectly dry sulphate of copper is white; the slightest moisture turns it blue. Muriate of cobalt is of a pale pink color; a very slight heat, by removing a little moisture, changes it to a green. These are a few instances selected from many which might be given. If we receive a prismatic spectrum on some papers, we have evidence that the molecular or chemical disturbance bears some relation to the color of each ray, or, in other words, that colored light so modifies the action of ENERGIA that the impression it makes is in proportion to the color of the light it accompanies, and hence there results a molecular arrangement capable of reflecting colors differently. Some instances have been given in which the rays impressed correspond with the colors of the luminous rays in a very remarkable manner.* One of the most decided cases is that of the paper prepared with the fluoride of soda and nitrate of silver. Sir John Herschel was, however, the first to obtain any good specimens of photographically impressed prismatic colorations. * See Mr. Hunt's "Researches on Light." It was noticed by Daguerre that a red house gave a reddish image on his iodized silver plate in the camera obscura; and Mr. Talbot observed, very early in his researches, that the red of a colored print was copied of a red color, on paper spread with the chloride of silver.** ** In 1842, I had shown me a picture of a house in the Bowery, which had been repaired a few days previous, and in the wall a red brick left. This brick was brought out on the Daguerreotype plate of precisely the same color as the brick itself. The same artist also exhibited to me, the full length portrait of a gentleman who were a pair of pantaloons having a blue striped figure. This blue stripe was fully brought out, of the same color, in the picture.--AMER. ED.