22 THE LAW OF PSYCHIC PHENOMENA.
revised his figures, and found that the supposed discrepancy did not exist. The last doubt in his mind having been thus set at rest, he gave to the world a theorem which rendered possible substantial progress in astronomical science.
In the field of psychological investigation a satisfactory working hypothesis has never been formulated. That is to say, no theory has been advanced which embraces all psychological phenomena. Many theories have been advanced, it is true, to account for the various classes of phenomena which have been observed. Some of them are very plausible and satisfactory to their authors when applied to a particular class of facts, but utterly fail when confronted with another class.
Thus, the students of the science of hypnotism are, and since the days of Mesmer have been, hopelessly divided into schools which wage war upon each other's theories, and dispute the correctness of each other's observations of facts. Mesmer's theory of fluidic emanations, which he termed "animal magnetism," seemed to account for the facts which he observed, and is still held to be substantially true by many votaries of this science. John Bovee Dods' electrical theorypositive lungs and negative blood was sufficiently plausible in its day to attract many followers, as it afforded a satisfactory explanation of many phenomena which came under his observation. Braid's physiological explanation of certain classes of the phenomena afforded, in his time, much comfort to those who believe that there is nothing in man which cannot be weighed in a balance or carved with a scalpel. In our own day we find the school of the Salpetriere, which holds that hypnotism is a disease of the nervous system, that its phenomena are explicable on physiological principles, that the suggestions of the operator play but a secondary role in their production, and that they can be produced, or successfully studied, only in diseased persons. On the other hand, the Nancy school of hypnotists holds that the science can be studied with profit only in perfectly healthy persons, and from a purely psy-