Part 6 (2/2)

Tones, or musical sounds, are produced by isochronous or equal-timed vibrations; thus _C_ of the first octave is produced by 256 vibrations a second, and if this tone is prolonged the vibration rate will continue uniformly the same Noises, on the other hand, are produced by vibrations which have no uniformity of vibration rate The ear's sensibility to pitch extends over about seven octaves The seven-octave piano goes down to 27-1/2 vibrations and reaches up to 3,500 vibrations

Notes of nearly 50,000 vibrations can be heard by an average ear, however, though these are too painfully shrill to be e of the ear is about eleven octaves The ear, having given us _loudness_ of tones, which depends on the amplitude of the vibrations, _pitch_, which depends on the rapidity of the vibrations, and _timbre_, or _quality_, which depends on the complexity of the vibrations, has no further qualities of sound to reveal

TASTE--The sense of taste is located chiefly in the tongue, over the surface of which are scattered many minute _taste-bulbs_ These can be seen as ses and at the tip of the tongue The substance tasted must be in _solution_, and cos The action of the stinizes the four qualities of _sour_, _sweet_, _salt_, and _bitter_ Many of the qualities which we improperly call tastes are in reality a complex of taste, sely to the sense of taste that many articles of food beco doses of medicine can be taken without discomfort if the nose is held

Probably none of us, if we are careful to exclude all odors by plugging the nostrils with cotton, can by taste distinguish between scraped apple, potato, turnip, or beet, or can tell hot milk from tea or coffee of the same temperature

SMELL--In the upper part of the nasal cavity lies a small brownish patch of s are located The substance saseous fors

Chemical action results in a nerve current

The sensations of smell have not been classified so well as those of taste, and we have no distinct names for them Neither do we kno many olfactory qualities the sense of s The only definite classification of smell qualities is that based on their pleasantness or the opposite We also borrow a few terrant_ odors and _fresh_ or _close_ smells There is some evidence e observe animals, or even prireater sensibility to certain odors, while at the same time there has been a loss of keenness of e call scent

VARIOUS SENSATIONS FROM THE SKIN--The skin, besides being a protective and excretory organ, affords a lodging-place for the end-organs giving us our sense of pressure, pain, cold, warmth, tickle, and itch

_Pressure_ seean the _hair-bulbs_ of the skin; on hairless regions small bulbs called the _corpuscles of Meissner_ serve this purpose _Pain_ is thought to be ans called the _bulbs of Krause_; and _warmth_ on the _Ruffinian corpuscles_

Cutaneous or skin sensation may arise from either _, from _thermal_ stimulation from hot or cold objects, from _electrical_ stimulation, or from the action of certain _chemicals_, such as acids and the like

Stiives us but two sensation qualities, _pressure_ and _pain_ Many of the qualities which we commonly ascribe to the skin sensations are really a coht pressure _Hardness_ and _softness_ depend on the intensity of the pressure _Roughness_ and _smoothness_ arise from interrupted and continuous pressure, respectively, and require h or smooth surface _Touch_ depends on pressure accompanied by the muscular sensations involved in the movements connected with the act Pain is clearly a different sensation from pressure; but any of the cutaneous or muscular sensations may, by excessive stimulation, be made to pass over into pain All parts of the skin are sensitive to pressure and pain; but certain parts, like the finger tips, and the tip of the tongue, are hly sensitive than others The skin varies also in its sensitivity to _heat_ and _cold_ If we take a hot or a very cold pencil point and pass it rather lightly and slowly over the skin, it is easy to discover certain spots from which a sensation of warmth or of cold flashes out In this way it is possible to locate the end-organs of temperature very accurately

[Illustration: FIG 17--Diagra distribution of hot and cold spots on the back of the hand C, cold spots; H, hot spots]

THE KINaeSTHETIC SENSES--The ive rise to perfectly definite sensations, but they have not been naans _Weight_ is the h the sensations connected with e _form_, _size_, and _distance_

THE ORGANIC SENSES--Finally, to the sensations mentioned so far ans of the body Froer_, _thirst_, and _nausea_; froans of sex come numerous well-defined but unna up the feeling-tone of our daily lives

Thus we see that the sensesat the outposts where nature and ourselves meet They discover the qualities of the various objects hich we come in contact and hand them over to the mind in the form of sensations And these sensations are the raw in to construct our ans of sense, especially good eyes and ears, therefore, are we able to enter fully into the wonderful world about us and receive the stiht and action

4 PROBLEMS IN OBSERVATION AND INTROSPECTION

1 Observe a schoolroo any that show defects of vision or hearing What are the symptoms? What is the effect of inability to hear or see well upon interest and attention?

2 Talk with your teacher about testing the eyes and ears of the children of so are easily applied, and the expense forWhat tests should be used? Does your school have the test card for vision?

3 Use a rotator or color tops fordiscs of white and black to produce different shades of gray Fix in ray made of half white and half black; three-fourths white and one-fourth black; one-fourth-white and three-fourths black

4 In the same way ray; reen in the same way Try various combinations of the four fundamental colors, and discover how different colors are produced Seek for these same colors in nature--sky, leaves, flowers, etc

5 Take a large wire nail and push it through a cork so that it can be handled without touching the ers Now cool it in ice or very cold water, then dry it and move the point slowly across the back of the hand Do you feel occasional thrills of cold as the point passes over a bulb of Krause? Heat the nail with a match flame or over a lamp, and perform the same experiment Do you feel the thrills of heat fro the nostrils with cotton and having soive you scraped apple, potato, onion, etc, and see whether, by taste alone, you can distinguish the difference Why cannot sulphur be tasted?

CHAPTER VII

PERCEPTION

No young child at first sees objects as we see them, or hears sounds as we hear theradual developrows day by day out of the learner's experience in his world of sights and sounds, and whatever other fields his senses respond to