Page:Popular Science Monthly Volume 47.djvu/542

 The discovery has well been called "the triumph of the last place of decimals"—that is, of work so exact that the worker knew that the small differences in the figures he obtained must be due to the presence of an unknown substance rather than to an error in his results. The prediction based on this observation, the search for the disturbing substance, and its discovery, form an achievement which, in the history of science, has perhaps only been surpassed by the prediction of Neptune by Adams and Leverrier, and its subsequent discovery by Galle.



OHN LOCKE, the physician and philosopher, long ago said that all our knowledge came from experience. Throughout his Treatise on the Human Understanding he develops this view of the acquisition of knowledge. This was followed by the writings of David Hume, the Scottish historian and metaphysician, who held that we knew nothing of objects in themselves, but only through their qualities; or, in other words, that we know of nothing but ideas. This was in turn followed by Immanuel Kant's Critique of Pure Reason, who took the ground that, though all our knowledge did not come from experience (as taught by Locke), yet it all came by experience. He held firmly to the ground that we had intuitions, or an a priori knowledge. It was this intuitive power that enabled us, by experience, a posteriori, to acquire knowledge of the qualities and of the forms of matter. Later came those who, like Ribot, Spencer, Romanes, have taught that there is no science of mind apart from the operations of the nervous system; that the operations of the brain constitute what is known as mental processes. Differing from these, the late T. H. Green held, as did Kant, that there is a science of ethics and psychology, independently of the study of physiology.

Fortunately for the purposes of this article, it will not be necessary to review the opinions of the above writers; it will not be necessary to prove which of the many views is correct. This much is definitely known: that certain physiological laws govern the human body, so as to determine what we know and how we came to know it. The intuitions of Kant, the common sense of Locke and Reid, the skepticism of Hume on knowledge, the idealism of Berkeley, need not detain us, as they have no special interest for the present. The object before us is to show that we 