POSSIBILITY OF PRODUCING NATURAL COLOURED PHOTOGRAPHS. 83

silver has been used. In the Philosophical Magazine for April, 1840,will be found a paper,—“ Experiments and Observations on Light whichhas permeated Coloured Media,”—in which I describe some curiousresults, on some of tlioso photographs which are prepared with theliydriodic salts, exposed to luminous influence with coloured fluids super-imposed; permitting, as distinctly isolated as possible, the permeationof the violet and blue,—the green, the yellow, and the red rays, undereach of which a complementary colour was induced. During Januaryof the present year, I prepared some papers with the bichromate ofpotash, and a very weak solution of nitrate of silver; a piece of thispaper was exposed behind four coloured glasses, which admitted thepassage respectively of, 1st, the violet, indigo, and blue rays; 2d, theblue, the green, and a portion of the yellow rays; 3d, the green, yellow,and orange rays; and, 4tli, the orange and red rays. The weather beingextremely foggy, tlio arrangement was unattended to for two days, beingallowed to lie upon a table opposite a window having a southern aspect.On examining it, it had under the respective colours become tinted , ofa blue, a green, and a red;—beneath the yellow glass the change wasuncertain, from the peculiar colour of the paper,—and this without asolitary gleam of sunshine. My numerous engagements have preventedmy repeating the observations I desire on this salt, which has hithertobeen considered absolutely insensible to light.

The barytic salts have nearly all of them a peculiar colourific effect;the muriate, in particular, gives rise to some most rich and beautifulcrimsons, particularly under the influence of light which has permeatedthe more delicate green leaves; and also in copying tho more highlycoloured flowers, a variety of tintings have been observed. We mayalways depend on producing a photographic copy of a leaf of a greencolour by the following arrangement:—Having silvered a copperplate,place it in a shallow vessel, and lay thereon the leaf of which a copy isdesired, maintaining it in its position by means of a piece of glass;pour upon it, so that the plate beneath the glass may be covered, a solu-tion of the hydriodato of potash, containing a little freo iodine—thenexpose the whole to sunshine. In about half an hour one of the mostbeautiful photographic designs which can bo conceived is produced, ofa fine green colour. Tho fluid is yellow, and cuts off nearly all the“ chemical ” rays, allowing only of tho free passage of the less re-frangible rays—tho most abundant being the yellow. This retards thoprocess of solarization; but it produces its complementary colour on theplate.

These facts will, I think, prove that the possibility of our beingenabled to produce coloured photographs is decided, and that the pro-bability of it is brought infinitely nearer, particularly by Sir John Her-schel’s very important discovery, than it was supposed to be.