ment that the same proportion holds if you make the weight in your hand heavier - i.e., if it be ten pounds, it will be necessary to add nearly ten ounces before you can detect the difference. Weber's Law. This fact illustrates a law that governs an immense multitude of facts. The Every one knows that in the stillness of night we hear things which are unperceived in the noise of day. gentle ticking of the clock, the distant bustle of the streets, the creaking of the chairs in the room impress themselves upon the ear. And every one knows that amid the confused hubbub of the market-place, or the roar of a railway train, we may lose what our neighbor is saying to us, or even fail to hear our own voice. The stars which shine so brightly at night are invisible by day; and although we can see the moon in the day-time, she is far paler than at night. Every one who has had to do with weights knows that if to a gramme in the hand we add a second gramme, the difference is clearly noticed; but if we add it to a kilogramme, there is no knowledge of the increase. "All these experiences are so common that we think them self-evident. Really, that is by no means the case. There can not be the least doubt that the clock ticks just as loudly by day as by night. In the clamor of the street, or amid the noise of the railway, we speak, if anything, more loudly than is usual. Moon and stars do not vary in the intensity of their light. And no one will deny that a gramme weighs the same whether it is added to one gramme or to a thousand. "The sound of the clock, the light of the stars, the pressure of the gramme weight, all these are sensation stimuli, and stimuli whose intensity always remains the same. What, then, do these experiences teach us? Evidently nothing else than this: that one and the same stimulus will be sensed as stronger or weaker, or not sensed at all, according to the circumstances under which it operates.1 But what kinds of change in the circumstances are there which can produce this alteration in sensation? On considering the matter closely, we discover that the change is everywhere of one kind. The tick of the clock is a weak stimulus for our auditory nerves, which we hear plainly when it is given by itself, but not when it is added to a strong stimulus of rattling wheels and all the other turmoil. The light of the stars is a stimulus for the eye; but if its stimulation is added to the strong stimulus of daylight, we do not notice it, although we sense it clearly when it is joined to the weak stimulus of twilight. The gramme weight is a stimulus for our skin which we sense when it is united to a present stimulus of equal strength, but which vanishes when it is combined with a stimulus of a thousand times its own intensity." Such facts make it necessary for us to qualify the conclusion suggested by the facts before considered, and say that, whenever the change produced by objects in the nervous system reaches a certain degree—in other words, when the new stimulus bears a certain ratio to the preexisting stimulus-that change will be followed by a change in the sensations. As the result of an immensely large number of experiments the figures which express this ratio in the several sense departments have been stated by Professor Wundt as follows: 1 Italics not in the original. In other words, if we represent the intensity of light acting upon the eyes at any time by 100, in order that a new light may be perceived, it must be at least as intense as 1 of the preceding light stimulus. If we are to hear a new sound in the midst of a pre-existing hubbub of noises, it must at least be as intense as of the pre-existing noise stimulus, and so on. This law is called Weber's law, because it was discovered by the physiologist Ernst Heinrich Weber. ex Are Sensations Always Regarded as Qualities of Objects? But an interesting question here arises: the question as to whether our sensations always wore the character they now bear the character of seeming to be what they are not objective qualities of objects, rather than subjective effects of these objects, produced through the nervous system; or whether in the beginning of our conscious life they appeared to be what they are periences of our own minds; or whether, indeed, they did not appear to be either, but were simply felt, in a vague indefinite way. A very slight observation of a new-born Ichild will be sufficient to convince us that his sensations do not seem to him as ours do to us. As we have seen already, it is probable that in the beginning of our mental life we have no definite sensations. Little by little, a child's sensations become definite; little by little, they are built up into the qualities and attributes of the external world. How is it done? That is a difficult question, the answer to which is the solution of the problem of perception. But before we can attempt to consider it, we must study two laws which play an important part in the matter -the law of habit and the law of the association of ideas. QUESTIONS ON THE TEXT. 1. Do you find yourself unwilling to believe that colors, sounds, etc., are sensations? 2. What are the sounds and colors spoken of by physics? 3. Show that our sensations are not copies of physical facts. 4. Mention other facts showing that what the world appears to us to be depends on changes in the nervous system. 5. Is every change in the nervous system followed by a change in the sensation? 6. What is Weber's law? State the evidence, so far as you know it, on which it is based. 7. Do a child's sensations seem to be qualities of objects? 8. What is the problem of perception? LESSON XX. THE LAW OF HABIT. We have already had occasion to notice some of the phenomena of habit. The child, at first unable to walk, then only a step or two and with great difficulty; the cyclist, at first obliged to give his entire attention to his wheel; the learner on the piano slowly spelling out the notes are cases in point. Child, cyclist, pianist, all acquire the skill which finally seems a sort of second nature through habit. Reid on Habit. Reid says: "As without instinct the infant could not live to become a man, so without habit man would remain an infant through life, and would be as helpless, as unhandy, as speechless, and as much a child in understanding at three-score as at three." Strong as this statement seems, it is probably an understatement of the truth. Without habit, we should rather say, a man would be as helpless, as speechless, as unhandy at three-score as at birth. Habit is the architect that builds the feeble rudimentary powers of the child into the strong, developed powers of the full-grown man. If a child's vague, purposeless movements give place to definite movements performed for definite purposes, if his sensations become more definite, if his perceptions become |