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The calotype pictures when prepared as we have stated, possess a yellowish tint, which impedes the process of taking copies from them. In order to remedy this defect, Mr. Talbot has devised the following method. The calotype picture is plunged into a solution consisting of hyposulphite of soda dissolved in about ten times its weight of water, and heated nearly to the boiling point. The picture should remain in about ten minutes; it must then be removed, washed and dried. By this process the picture is rendered more transparent, and its lights become whiter. It is also rendered exceedingly permanent. After this process the picture may be waxed, and thus its transparency increased. This process is applicable to all photographic papers prepared with solutions of silver. Having thus fully, and it is hoped clearly, considered the process, it may be necessary before dismissing the calotype from notice, to add one or two remarks from the observations and labors of some who have experimented in this art. Dr. Ryan in his lectures before the Royal Polytechnic Institution, has observed, that in the iodizing process the sensitiveness of the paper is materially injured by keeping it too long in the solution of iodide of potassium, owing to the newly formed iodide of silver being so exceedingly solvable in excess of iodide of potassium as in a few minutes to be completely removed. The paper should he dipped in the solution and instantly removed. There is another point, too, in the preparation of the iodized paper in which suggestions for a slight deviation from Mr. Talbot's plan have been made. In the first instance,