In natural history, in biological facts generally, it is not always easy to define the objects of study strictly, so as to classify them in a practical way. Dealing, however, with printed finger-patterns which are no longer living and changing things, we can hope to secure some of the advantages of a mechanical method. Verworn, in his _General Physiology_ (p. 71) says, very justly: “The fixing of sharp limits and definitions must contain, finally, a more or less arbitrary element, [that], indeed, all limits and definitions are only psychological helps towards knowledge.” Bearing this principle in mind, then, what is the end or object we aim at in a system of finger-print classification? The objects of identifying a person with some one who has had a name and left a history are of various kinds, as criminal, civil, military, naval, medical, legal, scientific, and insurance purposes. Now, in regard to the use of finger-prints for so many ends in view, a difficulty presents itself. It occurred to me at the outset of my studies, that if the system were to prove trustworthy and useful, even in a minor degree, immense numbers of people in civil life, in army, navy, and mercantile services, or under criminal conviction, would require to have their prints correctly classified, indexed, and arranged for easy reference. How could it be possible in so vast a collection or series of collections to find the one single record wanted? To ransack--unaided by a scientific method of classification--the register of an army containing some 500,000 soldiers would involve the search of a much larger number of cards or sheets than 500,000, according to the duration of regular service, and other possible conditions. To do this would obviously be quite as hopeless and futile a task as groping for a lost needle in a huge hay-field. The problem was to find a system which would facilitate the search in a _high degree_. Any mere slight assistance would still leave the essential problem unsolved. Now, we might have found in finger-prints mere variety without persistence, or mere persistence without initial variety, and in either case the study could yield little practical result. Again, mere diversity, however persistent, without some elements of underlying resemblance, would not have yielded a basis for such a methodic arrangement as was obviously required.