of Plato, the product of a more elementary sort of infant science, was made up of simpler contents than these; but still, when thus viewed, our science does indeed seem as if absorbed in the contemplation of a world of pure, — yes, I repeat, of Platonic ideas. For such realities get directly presented to no man’s senses.
But of course, on the other hand, we no sooner try to define the work of our science in these terms than we are afresh reminded that this realm of pure Platonic ideas would be a mere world of fantastic shadows if we had not good reason to say that these ideas, these laws, these principles, these ideal objects of science, remote as they seem from our momentary sensory experiences, still have a real and, in the end, a verifiable relation to actual experience. One uses the scientific conceptions because, as one says, one can verify their reality. And to verify must mean to confirm in sensory terms. Only, to be sure, such verification always has to be for us men an extremely indirect one. The conceived realities of constructive science, — atoms, molecules, ether-waves, geological periods, processes of change whose type is embodied in mathematical formulæ, — these are never directly presented to any moment of our verifying sensory experience. But nevertheless we say that science does verify these conceptions; for science computes that if they are true, then, under given conditions, particular sensory experiences, of a predictable character, will occur in somebody’s individual experience. Such predictions trained observers can and do successfully undertake to verify. The verification is
