Necessity of a Working Hypothesis. - The Newtonian Hypothesis. - The Atomic Theory. - A Psychological Hypothesis necessary. - Theories of Hypnotism and Mesmerism. - Spiritism. -Mental Therapeutics. - Liebault's Law of Suggestion. - Duality of Mind. - A Working Hypothesis for Psychology formulated. -Its Three Terms.

SUBSTANTIAL progress in any science is impossible in the absence of a working hypothesis which is universal in its application to the phenomena pertaining to the subject-matter. Indeed, until such an hypothesis is discovered and formulated, no subject of human investigation can properly be said to be within the domain of the exact sciences. Thus, astronomy, previous to the promulgation of Kepler's Laws and the formulation of the Newtonian hypothesis of gravitation, was in a state of chaos, and its votaries were hopelessly divided by conflicting theories. But the moment Newton promulgated his theorem a revolution began which eventually involved the whole scientific world. Astronomy was rescued from the domain of empiricism, and became an exact science. What the Newtonian hypothesis did for astronomy, the atomic theory has done Tor chemistry. It enables one skilled in that science to practise it with a certainty of results in exact proportion to his knowledge of its principles and his skill in applying them to the work in hand. He knows that if he can combine hydrogen and oxygen, in the proportion of two atoms of the former to one of the latter, water will be the result.

He knows that one atom, or part, of oxygen and one of carbon combined under heat will produce carbonic oxide, -a poisonous gas; that the addition of another atom, or part, of oxygen will produce carbonic anhydride (dioxide), - a harmless gas; and soon throughout the vast realm of chemical combinations.

The fact that the literal correctness of a given hypothesis is not demonstrable except by results, in no wise militates against its value in the domain to which it belongs. Indeed, it would cease to be a hypothesis the moment it were demonstrated. Newton's theorem is undemonstrable except from its results. Its correspondence, however, with every known fact, the facility with which astronomical calculations can be made, and the precision with which every result can be predicted, constitute a sufficient demonstration of its substantial correctness to inspire the absolute confidence of the scientific world. No one would hesitate to act in the most important concerns of life - nay, to stake his very existence - upon calculations based upon Newton's hypothesis. Yet there are not found wanting men who deny or doubt its abstract correctness. Volumes have been written to disprove it. But as no one has yet discovered a fact or witnessed a phenomenon outside of its domain, the world refuses to surrender its convictions.

When such a fact is discovered, then, and not till then, will there arise a necessity for revising the "Principia." It is a trite and true saying that one antagonistic fact will destroy the value of the finest theory ever evolved.

It is equally impossible to demonstrate the abstract correctness of the atomic theory. An appeal to the evidence found in uniform results is all that is possible to one who would give a reason for the faith that is in him. No one ever saw, felt; tasted, or smelled an atom. It is beyond the reach of the senses; nor is it at all probable that science or skill will ever be able to furnish instrumental aids capable of enabling man to take cognizance of the ultimate unit of matter. It exists for man only in hypothesis. Nevertheless, the fact remains, that in all the wide range of human investigation there is not a more magnificent generalization, nor one more useful to mankind in its practical results, than the atomic theory. Yet there are those who doubt its abstract correctness, and labor to disprove the existence of the atom. If the ultimate object of chemical science were to demonstrate the existence of the atom, or to seize it and harness it to the uses of mankind, it might be worth while to set the chemical fraternity right by demonstrating its nonexistence.

If the practice of chemistry on the basis of the theory were defective in its practical results, or failed in universal application, it would then be the duty of scientists to discard it entirely, and to seek a better working hypothesis.

The most that can be said of any scientific hypothesis is, that whether true in the abstract or not, everything happens just as though it were true. When this test of universality is applied, when no known fact remains that is unexplained by it, the world is justified in assuming it to be true, and in deducing from it even the most momentous conclusions. If, on the contrary, there is one fact pertaining to the subject-matter under investigation which remains outside the domain of the hypothesis, or which is unexplained by it, it is indubitable evidence that the hypothesis is unsafe, untrue, and consequently worthless for all practical purposes of sound reasoning. Thus, Sir Isaac Newton, after having formulated his theorem, threw it aside as worthless, for a time, upon making the discovery that the moon, in its relations with the earth, apparently did not come within the terms of his hypothesis. His calculations were based upon the then accepted estimate of the length of a degree of latitude. This estimate having been corrected by the careful measurements of Picard, Newton 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.