3. The next operation is to obtain the drawing. Having placed the Camera in front of the scene to be represented, and the lens being adjusted to the proper focus, the ground-glass of the Camera is withdrawn, and the prepared plate is substituted for it; and the whole is left till the natural images are drawn by the natural light from the object. The time necessary to leave the plate for a complete delineation of the objects, depends upon the intensity of the light. Objects in the shade will require more time for their delineation than those in the broad light. The full clear light of the south of Europe, Spain, Italy, and particularly, the more glowing brilliancy of tropical countries, will effect the object much more speedily than the duller luminosity of a northern clime. Some hours of the day are likewise more favourable than others. Daguerre states, that ‘the most favourable, is from 7 A.M. to 3 o’clock P.M., and that a drawing could be effected in Paris in 3 or 4 minutes, in June and July, which would require 5 or 6, in May and August, and 7 or 8 in April and September.’ In the progress of this art, at the present time, portraits and other objects are frequently delineated in the course of a few seconds. 4. Immediately after removing the plate from the Camera, it is next placed over the vapour of mercury, which is placed in a cup at the bottom of a box, and a spirit lamp applied to its bottom, till the temperature rise to 140 of Fahrenheit. This process is intended to bring out the image, which is not visible when withdrawn from the Camera; but in the course of a few minutes a faint tracery will begin to appear, and in a very short time the figure will be clearly developed. 5. The next operation is _to fix the impression_. In order to this, the coating on which the design was impressed must be removed, to preserve it from being decomposed by the rays of light. For this purpose, the plate is placed in a trough containing common water, plunging, and withdrawing it immediately, and then plunging it into a solution of salt and water, till the yellow coating has disappeared. Such is a very brief sketch of the _photogenic_ processes of Daguerre. Other substances, however, more easily prepared, have been recommended by Mr. Talbot, F.R.S., who appears, about the same time, to have invented a process somewhat similar to that of Daguerre. The following are his directions for the preparation of _Photogenic Paper_.