The senses, indeed, are not formed to enable man to solve the problems of Nature, but, as with the lower animals, merely to make existence possible, and, in a limited and incidental way, agreeable. And yet it is through these feeble senses that all human knowledge enters the brain, since all deductive reasoning must be based on previous inductive observation. More humiliating still, and more instructive in its relations to human testimony, is the lack of precision and power of appreciating details at long distances through the eye. At the interval of half a mile we are unable to recognize the countenance of our dearest friend; while ordinary type, in order to be read, must be held within a few inches of the face.
A recognition of the limitations of the sight—the king of the senses—makes the recognition of the limitation of the inferior faculties of hearing, smelling, tasting, and touching, easy and inevitable. Vibrations of the air below 32 per second, or above 100,000 per second, at the extreme, make no impression on the human ear; and, as experiments in the presence of audiences have proved, sensitive flames may react to atmospheric vibrations in perfect silence. Ordinary conversation is audible only within a few feet, while powerful-voiced orators in their mightiest efforts reach but a few thousands of people. The sense of smell is so restricted in its capacity that it fails to detect many of the most deadly poisons and causes of epidemics, and is of such slight practical service to man that patients who, through disease, have lost it entirely, sometimes say that they would not care to have it restored.
The sense of touch, of which all the other senses are supposed to be modifications, being of necessity limited to actual contact, is of no value in the study of anything at a distance.
It is clear, therefore, that the senses open but a few rooms in the infinite palace of Nature, and of these few they give us but feeble and imperfect glimpses. Throwing all questions of supernaturalism aside, it must be allowed that the senses bring us into direct relation with only an infinitesimal fraction of the natural; we are practically shut out of a knowledge of Nature, of which we are a part; hence the narrow limitations of human knowledge, all of which must be inductively based on what the senses are able to teach us, although the superstructure may by deduction be raised very high. The elementary and all-important facts in Nature are precisely those of which the senses, singly or combined, give us little information, or none whatever. The great forces—light, heat, electricity, gravity—can be studied in their effects only, not in themselves—in what they do rather than in what they are; hence it is that the great and central advances in science—the Copernican theory, the theory of gravitation, the wave-theory of light—are along the line of deductive, not inductive, investigation. If we depended on induction, we should know nothing of Nature, but would be blind babes wandering in a pathless forest. The first step in the evolution of any great science has ever been and must ever be the
