tion of the "original, certainty, and extent of human knowledge." Berkeley avowed that his motive, in investigating the nature of perception, was to provide a bulwark against the atheists. Hume is essentially theological, and in his "Inquiry concerning the Human Understanding," a section on Miracles stands side by side with one on the Idea of Necessary Connection. Reid wrote his "Essays on the Powers of the Human Mind" to refute Hume, and became, with this theological motive, the founder of Scotch psychology. Kant undertook his "Criticism of Pure Reason," and thus established a priori psychology, to show against Hume that the ideas of God, freedom, and immortality, could not be disproved by mere empirical reasoning. And the impulse which Hamilton, through Mansel, communicated to Psychology, by the new face he gave to the old problem of the Infinite, was a theological movement in its origin.
Under whatever name we give to it, under whatever form it may hereafter assume, Theology, the science of causes, essences, and origins, will play, as it has hitherto played, an important part in the development of the mental sciences, and especially of Psychology. When physical science is driving its ploughshare into untrodden regions till now only gazed down upon by the metaphysician in his balloon; when the speed of thought itself is measured; when the most complex effort of quantitative reasoning is proved to be fundamentally indentical with the simplest perception of relation; when the nature of intelligence is tracked upward in graduated sequence from the Radiata and Articulata to Newton and Shakespeare; and when the physical sides of all but the most subtle mental phenomena are being identified; the temptation is great to suppose that we are nearing the goal—that as so many laws of mind have been explained by physical laws, and so many facts interpreted in physical terms, the time is at hand, or at least will come, when the nature of causation, and of the substance of mind, and of the relation of phenomena to their source, and of that inscrutable source itself, will yield their secrets to the analysis of the inquirer armed with the weapons of physical science. Whatever power stands in the old place of Theology, which is dead—whether Metaphysics, if that be not dead also, or some "Unknowable" section of our compendiums of first principles—will show all such Comtist dreams to be vain, by eternally asking the unanswerable questions which it has been asking since the beginning of speculation. And each old question newly asked after each fresh advance of physical science tends to restore the equilibrium deranged by the operation of that dynamical factor, the history of the effects of which we will now, briefly sketch.
The application of physical methods to the phenomena of mind we believe to have originated in the fact that, outside the territory which (as we saw by the quotation from St. Thomas) was sacred to
