May I first say how deeply I feel the honour of being invited by the American Psychological Association, through its special committee, to deliver this lecture, and how grateful we are to Dr. and Mrs. Walter V. Bingham for their generosity in establishing such a lectureship. The problem which the founders had in mind happens to be one of special interest to us here in Britain; and it was with particular pleasure that we learnt that Mrs. Bingham and the committee had agreed that, on this occasion, the lecture should be given in this country and at this college. British psychologists, many of whom are gathered in this hall, are thus enabled to express their sincere and heartfelt admiration of the work carried out by Bingham himself, not only during two world wars, but also in time of peace, and not only in his own country, but also during his many visits over here. The valuable contributions that he made by his books, his numerous articles, and most of all perhaps by his tactful and untiring activities behind the scenes, I have already attempted to review elsewhere. Here therefore may I content myself with endorsing on behalf of British psychologists the well deserved tribute paid by Professor Egon Pearson on behalf of British statisticians.In his own autobiographical chapter Bingham has himself observed that one of his "chief functions in life seems to have been to act as an emissary for psychology to the heathen"; and it was during one of these apostolic missions that, when he came to London a year or two before the first world war, he so kindly sought me out to discuss the paper I had just published while at Oxford on the measurement and inheritability of mental capacity (3). It was my first effort at research, and the first paper published in this country on mental tests. I still treasure the letter I received from Ward of Cambridge, who was in those days the acknowledged leader of psychology in this country and editor of our new and only journal of psychology. While accepting my paper, he added that I was myself an outstanding example of wasted capacity, in that I had "spent so much time and industry on a transient problem like mental testing, which held so little promise for the future." "Evidently," said Bingham, "Oxford must begin by converting Cambridge." And it was the encouragement I then received from him that emboldened me to persevere. As it turned out, Bingham's precognition of the future of mental testing was far more accurate than Ward's; and soon afterwards McDougall at Oxford and Myers, then a young lecturer at Cambridge, succeeded in transforming British psychology from a branch of philosophy into a branch of science. In so doing both insisted that in future "psychology must devote itself to the study of the individual and not merely to the study of mind in general." 2 THE PROBLEM OP INDIVIDUAL DIFFERENCES than to ascertain and provide for the dull and defective.