MR. BALFOUR, in his Foundations of Belief, contends that naturalism is "deeply committed to the distinction between the primary and the secondary qualities of matter; the former (extension, solidity, and so forth) being supposed to exist as they are perceived, while the latter (such as sound and colour) are due to the action of the primary qualities upon the sentient organism, and apart from the sentient organism have no independent being." If this be so, he says, then, since nine tenths of our immediate experiences of objects are visual,' and since "all visual experiences, without exception, are, according to science, erroneous," it follows that, "regarded as sources of information, they are not merely occasionally inaccurate, but habitually mendacious." Whereas perception tells me that the rose-bud is pink and sweet-scented, naturalism, according to Mr. Balfour, denies that it is anything of the sort. The thing itself is not coloured. "As everybody knows, colour is not a property of the thing seen; it is a sensation produced in us by that thing." The rosebud shamelessly lies when it pretends to be coloured, whereas it is in reality only trembling with molecular vibrations. Colour and molecular vibrations belong to different orders of reality.

More recently, in his Presidential Address to the British Association at Cambridge (1904), Mr. Balfour asserts that "the aim of the physicist is to ascertain the nature of physical reality; a reality which may or may not be capable of direct perception, a reality which is in any case independent of it, a reality which constitutes the permanent mechanism of that physical universe with which our immediate empirical connection is so slight and so deceptive. That such a reality exists," he adds, "though philosophers have doubted, is the unalterable faith of science".

After briefly and lucidly sketching recent researches which have led up to the view that the physical nature of the atom reveals complex systems of electrical corpuscles, themselves perhaps due to knotted strains in the ether, Mr. Balfour permits himself to indulge in the following reflections:

Now the point to which I desire to direct attention is not to be sought in the great divergence between matter as thus conceived by the physicist and matter as the ordinary man supposes himself to know it, between matter as it is perceived and matter as it really is, but to the fact that the first of these two quite inconsistent views is wholly based on the second. This is surely something of a paradox. We claim to found all our scientific opinions on experience; and the experience on which we found our theories of the physical universe is our sense-perception of that universe. That is experience, and in this region of belief there is no other. Yet the conclusions which thus profess to be entirely founded upon experience are to all appearance fundamentally opposed to it ; our knowledge of reality is based upon illusion, and the very conceptions we use in describing it to others, or in thinking of it ourselves, are abstracted from anthropomorphic fancies, which science forbids us to believe and nature compels us to employ. The beliefs of all mankind about the material surroundings in which it dwells are not only imperfect but fundamentally wrong. It may seem singular that down to, say, five years ago our race has, without exception, lived and died in a world of illusions; and that its illusions, or those with which we are here alone concerned, have not been about things remote or abstract, things transcendental or divine, but about what men see and handle, about those "plain matters of fact" among which common-sense daily moves with its most confident step and most self-satisfied smile.

Such a position is scarcely satisfactory. One cannot but suspect that there is something not merely paradoxical but radically wrong in a doctrine according to which our common experience is wholly untrustworthy. Berkeley's outlook, much as it has been misunderstood, is saner, and may be so adapted to the existing condition of physical science as to comprise the results of modern physical science. On this view our daily and hourly experience, founded on direct perception, is not illusory, not fundamentally wrong, not mendacious, but eminently reliable and valid within its appropriate sphere. It is a guide to practical life, and our only criterion of its trustworthiness is that it enables us to meet all the varied requirements of that life. It affords the data on which, when submitted to physical analysis, may be founded a superstructure of physical conceptions not less reliable within their appropriate sphere. But these are themselves in terms of phenomena, and give us no more information than perception itself of the nature of a reality transcending human perception.

This transcendent reality is, however, just what Mr. Balfour claims as the result of recent physical theory. And he may perhaps secure the suffrages of the unwary when he says that "it is not only inconvenient but confusing to describe as 'phenomena' things which do not appear, which never have appeared, and which never can appear to beings so poorly provided as ourselves with the apparatus of sense-perception." It must be remembered, however, that the method of science, as I shall endeavour to show, is to carry to its ideal limit the curve of human perception. No one pretends that molecules and atoms, whatever may be their physical structure, can be perceived by man with the sensory endowment with which, for better for worse, he has to rest content. But I take it that the physicist believes them to be of the phenomenal order, and that they would be perceived by beings whose senses were indefinitely sharpened and extended in range of application. He endeavours to picture what would be the nature of our experience under these unattainable conditions. That is just why he has throughout his investigations to formulate his conclusions in terms of ideal construction. I seriously question whether any physicist of standing would accept Mr. Balfour's dictum that the conclusions which thus profess to be entirely founded on experience are in any sense fundamentally opposed to it. And I am convinced that the electrical theory of the atom helps in no way to bring us into relation with a different order of reality from that which is common to the whole range of our experience of natural things and events, and to the refined and extended range of physical science.