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water and dried. Thus prepared he calls it the io-gallic paper: it will remain good for a considerable time if kept in a press or portfolio. When required for use, it is washed with a solution of nitrate of silver (fifty grains to the ounce of distilled water), and it is then fit for the camera. Exposure in the Camera.--The calotype paper thus prepared possesses a very high degree of sensibility when exposed to light, and we are thus provided with a medium by which, with the aid of the photogenic camera, we may effectually copy views from nature, figures, buildings, and even take portraits from the shadows thrown on the paper by the living face. The paper may be used somewhat damp. The best plan for fixing it in the camera is to place it between a piece of plate glass and some other material with a flat surface, as a piece of smooth slate or an iron plate, which latter, if made warm, renders the paper more sensitive, and consequently the picture is obtained more rapidly. Time of Exposure.--With regard to the time which should be allowed for the paper to remain in the camera, no direct rules can be laid down; this will depend altogether upon the nature of the object to be copied, and the light which prevails. All that can be said is, that the time necessary for forming a good picture varies from thirty seconds to five minutes, and it will be naturally the first object of the operator to gain by experience this important knowledge. Bringing Out the Picture.--The paper when taken from the camera, which should be done so as to exclude every ray of light--and here