It is evident that all such attempts to solve a problem so complex as that of pessimism, even by the so-called exact methods of physiological psychology, cannot lead to any convincing result. Thus Kowalevsky’s different investigations led to contradictory conclusions. Whilst some of his series of facts supported the pessimistic conception, others were opposed to it, and he obtained no definite general conclusion. How can one expect to apply a method of measurement to sensations and emotions so different, not only from the qualitative point of view, but also in relation to their intensity? Take, for instance, the case of an individual who has experienced in one day nine sensations which were painful and one which was agreeable. According to the valuation of experimental psychologists, he ought to have reason to become a pessimist. However, this may be far from the case, if the nine painful impressions were much weaker than the single happy impression. The first were provoked by small wounds to his pride, fleeting pains of no importance, and small losses of money, whilst the happy emotion came from receiving a love letter. The sum of the ten impressions would be a happy one, and might well put him in an optimistic frame of mind. The learned attempts of experimental psychologists must be abandoned, as incapable of illuminating the problem. If, however, the human spirit still seeks some means of explaining the psychology of pessimism, there remains only the less subtle method given by the biographical study of human beings. III PESSIMISM IN ITS RELATION TO HEALTH AND AGE Relation between pessimism and the state of the health—History of a man of science who was pessimistic when young, and who became an optimist in old age—Optimism of Schopenhauer when old—Development of the sense of life—Development of the senses in blind people—The sense of obstacles