At a meeting of the British Association, Professor Grove described a process by which positive calotype pictures could be directly obtained; and thus the necessity to transfer by which the imperfections of the paper are shown, and which is moreover a troublesome and tedious process, is avoided. As light favors most chemical actions, Mr. Grove was led to believe that a paper darkened by the sun (which darkening is supposed to result from the precipitation of silver) might be bleached by using a solvent which would not attack the silver in the dark, but would do so in the light. The plan found to be the most successful is as follows: ordinary calotype paper is darkened till it assumes a deep brown color, almost amounting to black; it is then redipped into the ordinary solution of iodide of potassium, and dried. When required for use it is drawn over dilute nitric acid--one part acid to two and a half parts water. In this state, those parts exposed to the light are rapidly bleached, while the parts not exposed remain unchanged. It is fixed by washing in water, and subsequently in hyposulphite of soda, or bromide of potassium.

Mr. Grove also describes a process for converting a negative calotype into a positive one, which promises, when carried out, to be of great utility.

Let an ordinary calotype image or portrait be taken in the camera, and developed by gallic acid; then drawn over iodide of potassium and dilute nitric acid and exposed to full sunshine; while bleaching the dark parts, the light is redarkening the newly precipitated iodide in the lighter portions and thus the negative picture is converted into a positive one.

The calotype process has been applied to the art of printing, in England, but it possesses no advantages whatever over the method, with type, now so gloriously brought to perfection; and I can hardly think it will ever be made of any utility. For the benefit of the curious, however, I will give Mr. Talbot's method.

Some pages of letter-press are taken printed on one side only; and waxed, to render them more transparent; the letters are then cut out and sorted. To compose a new page lines are ruled on a sheet of white paper, and the words are formed by fixing the seperate letters in their proper order. The page being ready, a negative photograph is produced from it, from which the requisite number of positive photogenic copies may be obtained.

Another method, which requires the use of the camera, consists in employing large letters painted on rectangular pieces of wood, colored white. These are arranged in lines on a tablet or board, by slipping them into grooves which keep them steady and upright, thus forming a page on an enlarged scale. It is now placed before a camera, and a reduced image of it of the required size is thrown upon the sensitive paper. The adjustments must be kept invariable, so that the consecutive pages may not vary from one another in the size of the type. Mr. Talbot has patented his process, but what benefit he expects to derive from it, I am at a loss to determine.

Enlarged copies of calotype or Daguerreotype portraits may be obtained by throwing magnified images of them, by means of lenses, upon calotype paper.