20 THE LAW OF PSYCHIC PHENOMENA.
skilled in that science to practise it with a certainty of re-suits 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 3 and so on 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