I shall next touch briefly upon other diverse yet allied interests in Psychical Research, which may serve to illustrate further the various avenues of approach to this heterogeneous group of problems. I shall speak of these as the explanatory, the investigative, and the anthropological interests. The first is satisfied with finding out how alleged marvels are really performed; it takes up the physical phenomena of spiritualism or theosophy; it investigates conjuring tricks; it discovers the origin of noises in haunted houses; it ferrets out the means whereby mediums obtain knowledge of their sitters' private affairs. This is proper work for experts in prestidigitation and for detectives,--not for all such, for to be successful, the conjurer and the detective must have special knowledge and fitness for this branch of the trade. While the facts thus gathered may be useful as illustrative material to the psychologist, they form no essential part of his profession; nor is there any special reason why he should be best suited to determine the technical _modus operandi_ of such manifestations. That some psychologists with a strong interest in this type of phenomena might properly coöperate in such an investigation, if they chose, is too obvious to merit remark; but to trace out and expose trickery cannot be imposed upon the burdensome duties of the psychologist.
With a certain type of "psychical researcher" this explanatory interest is the dominant one; and by dispelling error and replacing false notions by true ones he may perform a useful service to the community. The explanatory interest is quite certain to be supplemented by the investigative, and that because the latter soon becomes necessary to the former. While the one is concerned with the explanation and description of the actual marvels accomplished, the other must consider also what is reported and what is believed to have been accomplished. The mechanism of a trick, whether brought forward as evidence of spiritualism or not, when clearly exhibited, explains the trick; a loose board under the roof, or the reflection from a lustrous surface, may at once reveal how mysterious noises and lights were really produced. But one must go farther to account for the recognition of relatives in the form of the medium covered with flimsy drapery, for the automatic spelling out of messages, or for the successes of guessing experiments. These two interests thus proceed hand in hand and furnish valuable material which the psychologist is ready to interpret and to utilize; for the study of how false beliefs spread, of how deception proceeds, teems with points of psychological significance. This, however, is by no means a unique characteristic of Psychical Research; there are also interesting psychological points in such diverse occupations as the actor's profession, in juggling and tricks of skill, in advertising, in religions revivals, etc. It is highly desirable that the materials thus gathered should be psychologically utilized, and it is equally desirable that such material should be collected. Many valuable studies in Psychical Research, which owe their origin not to a truly psychological interest but to this general explanatory and investigative interest, have incidentally brought to light material of great suggestiveness for the psychologist, and material which quite possibly would not otherwise have been discovered. I am more than willing to contribute whatever I can to the maintenance of a Coöperative Psychological Investigation Society which shall stand ready to take up the investigation of any phenomena which promise to yield data of psychological interest; which shall, however, keep far removed from any phase of the transcendental or the occult; which shall not feel itself under any obligation to _disprove_ any improbable or absurd hypothesis which this or that seeker for notoriety may choose to put forward; which shall not be dominated merely by the spirit of finding out whether there is "anything in" one movement or another, but will simply stand ready to supplement the work of the academic laboratories by undertaking, in the same spirit, a special form of investigation, which, under existing circumstances, such laboratories or their individual directors cannot expediently undertake.