class="x-ebookmaker-pageno" title="[Pg 67]"/> A century ago the case was very boldly put when we were asked to believe that the brain secretes thought as the liver secretes bile. Nobody to-day would think of making such a comparison, but it is more cautiously stated that consciousness is a "function" of the brain, or at all events of the nervous system, even as bile-making is a function of the liver. Before we yield any modicum of assent to this statement we may observe that "function" is a word with a wide range of meaning, and we must insist upon some closer definition. Here materialism calls to its aid the discovery of the correlation and equivalence of forces, one of the most stupendous achievements of our century. We now know that heat and light and electricity and actinism are not forces generically distinct and isolated each from the others. All are specific modes of molecular motion, transformable one into another at any moment as naturally as a cloud condenses into raindrops. Any such molecular motion, moreover, may come from the arrested visible motion of a mass, and may in turn be liberated so as to resume the form of visible motion, as when an electric current is transformed into the onward movement of the trolley car. The change in our conception of Nature that has been wrought by this wonderful discovery is more profound than all changes that went before. The balance in the hands of the chemist had already proved that no matter is ever lost but only transformed, and that every material form at any moment visible owes its existence to the metamorphosis of some previous form. So now it was further shown that the myriad properties or qualities of matter are simply the expression of myriads of activities which are all in a final analysis motions; that no motion is ever lost but only transformed, and that every kind of motion at any moment perceptible—whether in the form of movement through space, or of light, or heat, or electricity, or the actinism that builds up the green stuff in the leaves of plants—owes its existence to the metamorphosis of some previous kind of motion. Every living organism is a marvellous aggregate of divers forms of matter performing divers characteristic motions, and the sum total of these motions is the whole of life, as regarded purely on its physical side. When we take food we bring into the system sundry nitrogenous and hydrocarbon compounds, each of which is alive with little energies or latent capacities for certain kinds of motion. The oxygen of the air, especially in its unstable form of ozone, is a powerful inciter of chemical motions, and when we breathe it in, the little latent capacities presently become actual motions. Some of them are realized in the rhythmical movements of heart and lungs, some in the undulations that sustain the animal temperature, some in the formation of the tiny drops that collect in a secreting gland, some in the repair of tissue by the substitution of new complex molecules for old ones that are broken down, some in the contraction of a group of muscles, some in the changes within the substance of nerve that accompany conscious thought, sensation, and volition. Ah, yes, here we come to it at last! We do not doubt that all these myriad motions are members in a series of transformations, wherein the appearance of each results from the disappearance of its predecessors. We have neither the instruments nor the calculus to prove this in the infinite multitude of details, but the general theory has been so completely established wherever it is accessible to instruments and calculus that we can have no hesitation in granting its universality wherever matter and motion are concerned in any shape or amount. No scientific man will for a moment doubt that the little vibratory discharge between cerebral ganglia which accompanies a thought is one member in a series of molecular motions that might be measured and expressed in terms of quantity if we only possessed an apparatus sufficiently delicate and subtle.

Now if such is the case with the little physical motion within the brain, how is it with the accompanying thought? Does the correlation obtain between physical motions and conscious feelings? Are states of consciousness links in the Protean series of motions, in such wise that the vibration within the brain produces the thought or feeling? In other words is the thought or feeling merely a transformed vibration? Does a certain amount of vibration perish to be replaced by an exact equivalent in the shape of thought? and then does the thought perish in the act of giving place to other vibrations which end in a visible motion of muscles? as when, for example, you hear the sound of a bell and start toward the door.

On this point there has been much confusion of ideas. When I put the question to Tyndall in conversation, nearly thirty years ago, he seemed to think that there must be some such completeness of correlation between the physical and the psychical; but his mind was not at ease on the subject. Herbert Spencer, in his "First Principles," rather cautiously took the same direction and tried to show how a certain amount of motion might be transformable into a certain amount of feeling. He observed that the consciousness of effort or muscular strain in lifting a heavy weight is more intense than in lifting a light weight, and that when a loud sound sets up atmospheric vibrations of great amplitude the shock to our auditory consciousness is correspondingly greater than in the case of a gentle sound which sets up vibrations of small amplitude. But when he comes to the inner regions of thought and emotion which are not reached by percussion and strain, he is less successful in finding illustrations. It is especially worthy of note that in the final edition of "First Principles," published in this year 1900 and in Spencer's eighty-first, he goes very far toward withdrawing from his original position, while in his Preface he calls attention to this change as one of the most important in the book. In my "Cosmic Philosophy," published in 1874, I maintained that to prove the transformation of motion into feeling or of feeling into motion is in the very nature of things impossible. In order to be convinced of this, let us go back a few years and ask how the great doctrine of the correlation of forces became established. Its first absolute verification occurred about 1846, when Dr. Joule showed "that the fall of 772 lbs. through one foot will raise the temperature of a pound of water one degree of Fahrenheit."[2] When this was proved it gave us the mechanical equivalent of heat, and the theory acquired a truly scientific character. Similar quantitative correlations were established in the case of heat and chemical action by Dulong and Petit, and in the case of chemical action and electricity by Faraday. The truth of the theory is wholly a question of quantitative measurement. Now you can measure heat, you can measure electricity, and since the action of nerves in all probability consists of undulatory motions it is to some extent measurable, and doubtless would be completely measurable had we the means. But when you come to thoughts and emotions, I beg to know how you are going to work to give an account of them in foot-pounds! It is not simply that we have no means at hand, no calculus