The artist’s word for representing the successive planes is perspective. If you stand between the rails of a trolley line or railroad and look along it, the lines seem to draw together or converge. Yet in reality you know that they are equidistant from each other all the way along. But, since our power of seeing becomes less and less as objects are farther removed from us, so to our diminishing sight the size and distinctness of the space between the rails appears also to diminish. In the same way you will observe that the width of the street seems to diminish, and the people and wagons appear smaller and smaller, according as they are seen farther and farther back in the successive planes. The houses, too--you know that if you stood in front of any of the houses, exactly facing it, the upright sides would appear to be, as they are, of equal height, and that the windows and cornice would appear in parallel horizontal lines. Yet, as you stand in the street and look along the houses on either side, they present a different appearance. In the case of each house the upright side, nearer to you, seems higher than the one farther off, and the rows of windows and the line of the cornice appear to slope downward. For the houses as they take their places in the receding or successive planes seem to diminish in size.