The positive is left in this solution till the required tint is obtained, when it is to be placed in plain hypo. two ounces to the pint, and in about a quarter of an hour transferred to a basin of pure water, and well washed in several waters. The other detail of MR. POLLOCK's process is so admirably and clearly given, and so like that I pursue, that I will not trouble your columns with it again. The after-bath of pure hypo. is not absolutely necessary; and where it is desired to obtain fine olive, and dark sepia, and black tints, a better tone results from washing well, long, and frequently, with water alone. This bath also gives very rich tints with paper, prepared without albumen: viz.-- Chloride of ammonium 5 grs. Water 1 oz. Lay the paper on this, and then hang it up to dry, and excite with ammonio-nitrate containing seventy grains of nitrate of silver to one ounce of water. Should the above solution not give the requisite tints soon after being made, add more chloride of silver; but bear in mind that the solution will then soon become saturated when setting positives, and when this occurs it must be rectified by the addition of a small portion of fresh hypo. alone. F. MAXWELL LYTE. P.S.--I may add that I have only lately tried the addition of the iodide of potassium to my setting liquid, and so must qualify my recommendation of it by saying so. Florian, Torquay. _Stereoscopic Angles._--I am obliged to MESSRS. SHADBOLT and WILKINSON for the information given in reply to my Queries (Vol. vii., p. 505.) My mode of operation is precisely that of MR. WILKINSON: "I obtain all the information I can from every source; then try, and judge for myself." Hence the present letter.