PRISMATIC ANALYSIS.--The most refrangible portion of the spectrum, (on a Daguerreotype plate) appears, after the plate has been exposed to the vapor of mercury, to have impressed its colors; the light and delicate film of mercury, which covers that portion, assuming a fine blue tint about the central parts, which are gradually shaded off into a pale grey; and this is again surrounded by a very delicate rose hue, which is lost in a band of pure white. Beyond this a protecting influence is powerfully exerted; and notwithstanding the action of the dispersed light, which is very evident over the plate, a line is left, perfectly free from mercurial vapor, and which, consequently, when viewed by a side light, appears quite dark. The green rays are represented by a line of a corresponding tint, considerably less in size than the luminous green rays. The yellow rays appear to be without action, or to act negatively, the space upon which they fall being protected from the mercurial vapor; and it consequently is seen as a dark band. A white line of vapor marks the place of the orange rays. The red rays effect the sensitive surface in a peculiar manner; and we have the mercurial vapor, assuming a molecular arrangement which gives to it a fine rose hue; this tint is surrounded by a line of white vapor, shaded at the lowest extremity with a very soft green. Over the space occupied by the extreme red rays, a protecting influence is again exerted; the space is retained free from mercurial vapor and the band is found to surround the whole of the least refrangible rays, and to unite itself with the band which surrounds the rays of greatest refrangibility. This band is not equally well defined throughout its whole extent. It is most evident from the extreme red to the green; it fades in passing through the blue, and increases again, as it leaves the indigo, until beyond the invisible chemical rays it is nearly as strong as it is at the calorific end of the spectrum. Images on Daguerreotype plates which have been completely obliterated by rubbing may be restored, by placing it in a tolerably strong solution of iodine in water. BROMIDE OF SILVER.--This salt, like the iodide, does not appear to be readily changed by the action of light; but when combined with the nitrate of silver it forms a very sensitive photographic preparation.