Aerial perspective has not been sufficiently attended to by the painters of pictorial backgrounds. There are many other subjects in connection with art and photography that might be discussed with advantage--such as composition, arrangement of accessories, size, form, character, and fitness of the things employed; but I leave all these for another opportunity, or to someone more able to handle the subjects. For the present, I am content to point out those errors that arise from neglecting true perspective, and while showing the cause, distinctively supply a remedy. It is not the fault of perspective in the background where the lines are not in harmony with each other--these too frequently occur, and are easily detected--but it is the error of painting a pictorial background as if it were an independent picture, without reference to the conditions under which it is to be used. The conditions of perspective are determined by the situation of the lens and the sitter. If the actual objects existed behind the sitter, and were photographed simultaneously with the sitter, the same laws of perspective would govern the two. What I urge is, that if, instead of the objects, a representation of them be put behind the sitter, that representation be also a correct one. The laws of perspective teach how it may be made correctly, and the starting point is the position of the lens in relation to the sitter. Some may say that these conditions of painting a background cannot be complied with, as the lens and sitter are never twice exactly in the same relation to each other. There is less force in this objection than at first appears. Each photographer uses the same lens for all his _carte_ portraits--and pictorial backgrounds are very frequently used for these--and the height of his camera, as well as the distance from his sitter, are so nearly constant, that the small amount of errors thus caused need not be recognized. If the errors that exist were not far more grave, there would be no necessity for this paper. Exceptional pictures should have corresponding backgrounds.