For the readers of a journal devoted to the application of mathematics to psychological research it is scarcely necessary to spend much time in answering the question, “Why mathematics?” Science may best be defined as that set of postulates regarding experience to which the universal assent of competent observers may be obtained, plus the organization of such postulates into theories for which universal assent is likewise obtainable. Of all the propositions about nature those concerned with mathematics are most readily given universal assent. From this state of affairs the Kantian aphorism that a discipline is as scientific as it contains mathematics is entirely consequent. Kant himself doubted the applicability of mathematics to psychology and so was led to question the possibility of a scientific psychology. Fechher, as is well-known, thought differently and from Fechner‘s day the application of mathematical procedures has become an increasingly important part of psychological research until to-day we have a journal devoted to such application alone.