We consider ourselves at this present time competent to set up a photographic ambulance or to hang out a sign in any modest country town. We should, no doubt, over-time and under-tone, and otherwise wrong the countenances of some of our sitters; but we should get the knack in a week or two, and if Baron Wenzel owned to having spoiled a hat-full of eyes before he had fairly learned how to operate for cataract, we need not think too much of libelling a few village physiognomies before considering ourselves fit to take the minister and his deacons. After years of practice there is always something to learn, but every one is surprised to find how little time is required for the acquisition of skill enough to make a passable negative and print a tolerable picture. We could not help learning, with the aid that was afforded us by Mr. Black and his assistants, who were all so very courteous and pleasant, that, as a token of gratitude, we offered to take photographs of any of them who would sit to us for that purpose. Every stage of the process, from preparing a plate to mounting a finished sun-print, we have taught our hands to perform, and can therefore speak with a certain authority to those who wish to learn the way of working with the sunbeam. Notwithstanding the fact that the process of making a photographic picture is detailed in a great many books,--nay, although we have given a brief account of the principal stages of it in one of our former articles, we are going to take the reader into the sanctuary of the art with us, and ask him to assist, in the French sense of the word, while we make a photograph,--say, rather, while the mysterious forces which we place in condition to act work that miracle for us. We are in a room lighted through a roof of ground glass, its walls covered with blue paper to avoid reflection. A camera mounted on an adjustable stand is before us. We will fasten this picture, which we are going to copy, against the wall. Now we will place the camera opposite to it, and bring it into focus so as to give a clear image on the square of ground glass in the interior of the instrument. If the image is too large, we push the camera back; if too small, push it up towards the picture and focus again. The image is wrong side up, as we see; but if we take the trouble to reverse the picture we are copying, it will appear in its proper position in the camera. Having got an image of the right size, and perfectly sharp, we will prepare a sensitive plate, which shall be placed exactly where the ground glass now is, so that this same image shall be printed on it.