ABSTRACT
The experimenter meets with serious difficulties when he tries to work with complex objects like pictures. The essential nature of experiment is that we should vary the conditions and trace the varying consequences to those varying conditions. Now it is comparatively easy to do this in the case of simple colours and figures. But to change one picture for another may be to introduce a host of differences; and also the effect of a picture on a subject may be so complex that he himself may be misled in saying what elements in the picture appeal to him most. It is therefore not surprising that much still remains to be done in the way of experiments with pictures. Nevertheless many aspects have already been investigated.
