In the following notes on some of the pictures in the National Gallery, it is not my intention to assume the character of an art-critic, but simply to record the impressions produced on the mind of a photographer while looking at the works of the great old masters, with the view of calling the attention of photographers and others interested in art-photography to a few of the pictures which exhibit, in a marked degree, the relation of the horizon to the principal figures. During an examination of those grand old pictures, two questions naturally arise in the mind: What is conventionality in art? and--In whose works do we see it? The first question is easily answered by stating that it is a mode of treating pictorial subjects by established rule or custom, so as to obtain certain pictorial effects without taking into consideration whether such effects can be produced by natural combinations or not. In answer to the second question, it may be boldly stated that there is very little of it to be seen in the works of the best masters; and one cannot help exclaiming, "What close imitators of nature those grand old masters were!" In their works we never see that photographic eye-sore which may be called a binographic combination of two conditions of perspective, or the whereabouts of two horizons in the same picture. The old masters were evidently content with natural combinations and effects for their backgrounds, and relied on the rendering of natural truths more than conventional falsehoods for the strength and beauty of their productions. Perhaps the simplest mode of illustrating this would be to proceed to a kind of photographic analysis of the pictures of the old masters, and see how far the study of their works will enable the photographer to determine what he should employ and what he should reject as pictorial backgrounds in the practice of photography. As a photographer, then--for it is the photographic application of art we have to consider--I will proceed to give my notes on pictures in the National Gallery, showing the importance of having the horizontal line in its proper relation to the sitter or figure.