The Inductive Principle, considered either as a Process or a Method, is valuable, therefore, mainly as it furnishes proper starting points for the activity of the Deductive Principle. Thus far in the history of the Natural Sciences it has been the best and safest guide in affording such starting points. But the indications are numerous all about us that the progress of Scientific discovery will ere long bring us to a stage, where the Laws or Principles which underlie every department of the Universe being fully revealed, the function of the Inductive Principle as a guide to fundamental bases, will be at an end, and the Deductive Method once more assume the leadership, opening to us all departments of investigation, with the rapidity, precision, and certainty which characterize Mathematical research and Demonstrative Reasoning. This _desideratum_ must necessarily result whenever a Unitary Law shall be discovered in Science; whenever the Sciences, and the Phenomena within the different Sciences, shall be _basically_ connected. All the present conditions and tendencies of knowledge indicate that the attainment of this crowning intellectual goal was predestined to our epoch. It has been the grand work of the Inductive Method to arrange Facts under Principles, and these latter as Facts or Truths under a smaller number of Principles, and these in turn under a still smaller number, until all the Phenomena of the different domains of thought which are reckoned as Sciences are included within a few Principles which lie at the foundation of each domain. The connection of these few Principles by a still more fundamental Law, is all that is necessary to the completion of the work of the centuries and the establishment of a Universal or Unitary Science. Already those recognized as leaders in the Scientific world watch expectantly the signs of the times and await the advent of the Grand Discovery which is to usher in a new intellectual era, 'We have reached the point,' says Agassiz, in one of his _Atlantic Monthly_ articles, 'where the results of Science _touch the very problem of existence, and all men listen for the solving of that mystery_. When it will come, and how, none can say; but this much, at least, is certain, _that all our researches are leading up to that question_, and mankind will never rest till it is answered.'