Science has certainly seemed to be justified by success. Indeed it is difficult even to imagine that its great advance in modern times could have been achieved had it chosen any other method. That it should be untrammelled by irrelevance was a condition of development. It is by narrowing inquiry, by concentrating observation, by excluding larger issues, by dividing and subdividing that it has conquered. But there is a limit, and the very advance of science, by its own method, and on its chosen conditions, has brought it face to face with the philosophical problem it set out by ignoring. It finds itself after a century of continuous triumphant progress arrested, not by the clamour of philosophers, but by the empirical discoveries of its own researchers, and forced to revise its apparently workable hypothesis that knowing is not anything. If science is discovery it must at least be of some consequence to know who or what it is that discovers and what are the conditions of discovery. A revolution once started has a way of gathering momentum and goes on completing itself. And to-day science from its old attitude of regarding knowing as not anything is fast coming to regard it as everything.

The revolution has come with dramatic suddenness, but like all revolutions it has been long preparing. Its fall of the Bastille was the verification of Einstein's calculation of the shift of the stars, observed during the total eclipse of May 29, 1919. This proved that the path of the light rays is curved in a gravitational field, and rendered meaningless the hypothesis of homoloidal space. But though the revolution has been sudden the scientific world was ripe for it. For many years and in many directions the old bedrock materialism, on which science had hitherto builded, was seen to be cracking and crumbling. Along several lines the sciences have been steadily converging on the necessity of a complete revision of their fundamental principle.

First, there stands the doctrine of Berkeley. More and more as science has advanced it has become obvious to scientific thinkers that this doctrine cannot be ignored but

must be reckoned with. It is easy enough to make a definite and clear distinction between the concepts of scientific reality and the percepts of sensible experience, but is it not evident that these percepts of the senses are the immediate objects of knowledge? How then do we pass from these subjective sensible qualities to the objective concepts of the scientific reality? What is the relation between the one and the other? When we have systematically worked out our concept of the scientific reality with its unsensed mathematical properties can we say that it is full reality, and that the colours, sounds, tastes, smells, feelings, which make up our experience of reality, are not anything, a shadow world of mere illusion? We must admit that they are something, but if they are something may they not, must they not, be everything? This problem of the status of sensations and their exact position in the scheme of physical reality has particularly engaged the physicists. They by their truly magnificent generalizations enable us to form images of physical reality which represent a universe absolutely indifferent to consciousness; a world, for example, in which light, electricity, magnetism, and the rest are independent completely of the colour, sound, feeling by which they are known, and which would be what they are even were there no consciousness and, therefore, no sensible quality to be experienced. But then these sensations and the sensible qualities of which they are the experience are de facto existence. What place and what role is to be assigned to them in physical theory? One character of them is that of being subjective responses to objective stimuli, but that does not prevent them being objective in the full scientific meaning. As they could not be accommodated in the general materialistic or naturalistic conceptions of physics, it was supposed that they could be side-tracked, and for this purpose the physicists had recourse to the philosophers. Sensations, and, generally, the sensible qualities which they imply, were declared to be epiphenomena, a euphonious way of saying they are nothing; or they were recognized as existent facts but declared to belong to an independent and parallel series having no

relations of interaction with the physical series. This makeshift theory could not work, but it seemed to serve a purpose, and at least to enable science to guard the pure objectivity of its subject-matter. It broke down completely when science recognized the failure of all attempts to determine the movement of a system by observations within the system. This brought out with sudden clearness that the activity of the observer is an essential determinant factor of the nature of the physical fact itself. The principle of relativity is the abandonment of the attempt in science to dissociate act and fact.

A second line along which science, following its own method and holding fast to its distinctively objective principle, has found its own progress bring it into conflict with its own principle, is in the scientific concept of life. The biological sciences arose under a kind of rational protest against the superstitious idea that life is a mystery,the tree of life planted by God in Eden,-something linking us with the supernatural and the divine, which it is impious to investigate scientifically. The rapid success of biology seemed at first to be wholly due to the application of the mechanistic concepts of physics. So much so that a few years ago all biologists believed we might be on the point of demonstrating the complete success of the scientific method by the synthetic production of living matter in a chemical laboratory. The outstanding feature of the scientific attainment of the nineteenth century is the Darwinian theory of evolution by natural selection, that is, by a selection conceived purely naturalistically as a survival of the fittest. But without any relapse into finalistic and teleological categories, hateful to the scientific spirit, the progress of biological science, following its own line of investigation, has suggested, -and brought increasing certainty to the suggestion, that the intellect is itself a product of evolution. The study of instinctive action, and of purposive action generally, tends increasingly to confirm it. But if intellect is a product of evolution the whole mechanistic concept of the nature and origin of life is absurd, and the principle which science has adopted must clearly be revised. We have only to state it to see

the self-contradiction. How can the intellect, a mode of apprehending reality, be itself an evolution of something which only exists as an abstraction of that mode of apprehending, which is the intellect? If intellect is an evolution of life, then the concept of the life which can evolve intellect as a particular mode of apprehending reality must be the concept of a more concrete activity than that of any abstract mechanical movement which the intellect can present to itself by analysing its apprehended content. And yet further, if the intellect be a product of the evolution of life, it is not absolute but relative to the activity of the life which has evolved it; how then, in such case, can science exclude the subjective aspect of the knowing and build on the objective presentation as an absolute ? Clearly the biological sciences necessitate a reconsideration of the scientific principle.

A third line is that of the criticism of the foundation of the mathematical sciences. If not more important than the other lines it has certainly been more decisive. It has led to the formulation of the general principle of relativity, and this has involved a complete revolution in our notions of the structure of the universe and necessitated the entire re-formation of our concepts of space, time and matter. Scepticism in regard to the postulates of the mathematical sciences has been until quite recent times purely theoretical, never seeming even to threaten to justify itself in any practical application. Indeed it has seemed eminently the occupation of highly speculative minds, detached completely from any practical interests, or else the attraction of writers of romance attempting to rationalize the creations of a fertile imagination. Those, for example, who in the past have speculated on the possibility of a fourth dimension of space, or of a reversal of the order of temporal succession, have been moved to it either by their interest in theories of personal survival or purely spiritual existence, and their satisfaction in the result of such speculations has been due rather to comfort in the suggestion of possibilities, than to attainment in the discovery, or hope of discovery, of fact. But meanwhile a steady progress of purely scientific investi

gation has led to a new cosmogony and a new theogony based on a new metaphysic of physical reality. Let us indicate briefly the lines of this development.

First, we may notice the entirely modern research which has led to the mathematical theory of continuity. Mathematics is the typical exact science, conceived by us as essentially true without depending in any manner on subjective opinion. Yet at its very basis it is challenged to justify its affirmation of the reality of the continuum on which its propositions depend and in regard to which alone its propositions have meaning and are true. What is the relation between the physical continuum which is based on our perceptions of reality and the mathematical continuum of which there are no perceptions but which we construct conceptually from the implications of sensible perception? In its origin the mathematical continuum is the attempt to rationalize a common contradictory experience. A certain sense-given particular A (a shade of colour, a musical note, a feeling of push or resistance) is indistinguishable from a numerically different particular B, and B in like manner is indistinguishable from C, yet A is distinguishable from C. For example, a shade of green in a colour scale may be indistinguishable by perception from the shade below and the shade above, while yet the difference of these two is clearly perceptible. To harmonize this discrepancy and reconcile it with the logical principle of contradiction, we suppose that behind the physical continuum which we perceive there is a real or mathematical continuum of which the physical continuum is only an imperfect apprehension, and we seem to find abundant proof of this in experience itself in the instruments devised to increase the discerning powers of the sense-organs. It is the triumph of modern mathematics to have shown the mode in which the mind constructs this continuum. It consists not of atoms or electrons or ether, but of points, lines, planes, and it has become conceptual space, the subject-matter of the science of geometry. The infinite divisibility of the mathematical continuum, which has been from ancient times the fruitful origin of antinomies of