But, now, what is the error of the "naturalist"? Simply that he has converted the scientific doctrine into an ontological doctrine. He really knows nothing, and cannot possibly know anything, about his atoms, except just this, that they give the law of the phenomena. He has nothing whatever to say to them in any other relation. If he proceeds, as Mr. Balfour says that he proceeds, to declare that nothing exists except atoms, that they are the ultimate realities, that they are "things in themselves," or objects independent of any subject, he is going beyond his tether, passing from science to transcendental metaphysics, and getting into hopeless confusion. In fact, after he has done his worst we may still follow Berkeley and deny the existence of matter, or declare with Clifford that atoms are only bits of mindstuff, or adopt any other metaphysical theory we please. The atoms at most are things which we judge from the analogy of the senses; and it is a pure illusion to suppose that they can ever take us into an extra-sensible world. They represent not only a convenient but an indispensable contrivance for enabling us to formulate scientific laws, such as those of light and heat; but they take us no further. In a remarkable passage, Mr. Balfour sketches an analogy, which gives the application of this to philosophical or theological questions; and I will venture to give my own interpretation of the argument because it seems to lead to the real point. We believe, he says, in a scientific theory of heat, although our view of the "realities" has changed. People once thought that heat was a substance. They now hold it to be a mode of motion. Yet our "scientific faith" (our faith, I suppose, that things are hot, and that their heat varies according to certain assigned laws) remains unaffected. On the other hand, he says, if we cease to believe in the Christian doctrine of the atonement, we cease also to have that "sense of reconciliation" between God and man which the doctrine was intended to explain. This he seems to regard as a kind of melancholy paradox. Why is the scepticism harmless in science and fatal in theology? First, what are the admitted facts? A man of science propounds a theory of heat. If his theory does not give us the observed laws, we reject it and adopt a more successful theory. In any case, we, of course, continue to believe in heat. We may know facts without knowing their causes; as, for example, the fact of gravitation, which is not the less certain because it is at present an ultimate fact. Otherwise our knowledge would be limited indeed; for even if the cause (in the scientific sense) were given, we should still have to ask, what is the cause of that cause? If heat is due to certain systems of atoms, we might still inquire how the atoms came to occupy their places, and possess the properties which they actually have. An effect "depends upon" a cause, as we naturally say; but it does not follow that the