This is Volume II of twenty-one in a series of Cognitive Psychology. Originally published in 1938. The war, differences of tongue, sentiment, and background all contributed towards making it difficult for English-speaking readers to welcome what they were the experimental methods and results of certain German psychologists. The gap thus created was not bridged until very recent times: notably by the publication in 1935 of Professor K. Koffka’s Principles of Gestalt Psychology. Even this important work, however, does not wholly effect the necessary transition from the German psychology of 1912 to the present day, and Professor Koffka himself mentions this in a Preface footnote of his book. The present volume is offered in the hope that it may play a part in completing the structure.