Chapter XXII: Part 22

The wood used in pencil making must be close and straight grained, soft, so that it can readily be whittled, and capable of taking a good polish. No better wood has been found than the red cedar, a native of the United States, a durable, compact and fragrant wood to-day almost exclusively used by pencil makers the world over. The best quality is obtained from the Southern States, Florida and Alabama in particular.

The wood is cut into slats about 7 inches long, 2¹⁄₂ inches wide, and ¹⁄₄ inch thick. It is then thoroughly dried in kilns to separate the excess of moisture and resin and to prevent subsequent warping. After this the slats are passed through automatic grooving machines, each slat receiving six semi-circular grooves, into which the leads are placed, while a second slab with similar grooves is brushed with glue and covered over the slat containing the leads. This is passed through a molding-machine, which turns out pencils shaped in the form desired, round, hexagon, etc. The pencils are now passed through sanding machines, to provide them with a smooth surface.

How is the Color Put on the Outside of the Pencil?

After sand-papering, which is a necessary preliminary to the coloring process, when fine finishes are desired, the pencils are varnished by one of several methods. That most commonly employed is the mechanical method by which the pencils are fed from hoppers one at a time through small apertures just large enough to admit the pencil. The varnish is applied to the pencil automatically while passing through, and the pencils are then deposited on a long belt or drying pan. They are carried slowly a distance of about twenty feet, the varnish deposited on the pencils meanwhile drying, and are emptied into a receptacle. When sufficient pencils have accumulated, they are taken back to the hopper of the machine and the operation repeated. This is done as often as is necessary to produce the desired finish. The better grades are passed through ten times or more. Another method is that of dipping in pans of varnish, the pencils being suspended by their ends from frames, immersed their entire length and withdrawn very slowly by machine. A smooth enameled effect is the result. The finest grades of pencils are polished by hand. This work requires considerable deftness; months of practice are necessary to develop a skilled workman. After being varnished, the pencils are passed through machines by which the accumulation of varnish is sand-papered from their ends. The ends are then trimmed by very sharp knives to give them a clean, finished appearance.

Stamping is the next operation. The gold or silver leaf is cut into narrow strips and laid on the pencil, whereupon the pencil is placed in a stamping press, and the heated steel die brought in contact with the leaf, causing the latter to adhere to the pencil where the letters of the die touch. The surplus leaf is removed, and, after a final cleaning the pencil is ready to be boxed, unless it is to be further embellished by the addition of a metal tip and rubber, or other attachment.

How is the Eraser Put On a Pencil?

In this country about nine-tenths of the pencils are provided with rubber erasers. These are either glued into the wood with the lead, or the pencils are provided with small metal ferrules threaded on one end, into which the rubber eraser-plugs are inserted. These ferrules are made from sheet brass, which is cupped by means of power presses, drawn through subsequent operations into tubes of four- or five-inch lengths, cut to the required size, threaded and nickel-plated.

Courtesy of Doubleday, Page & Co.

A SOUTHERN COTTON FIELD]

The Story in a Bale of Cotton

Where Does Cotton Come From?

We get cotton from a plant which grows best in the warm climate of our Southern States. Cotton has been known to the people of the world for a long time. Before the birth of Christ people knew about cotton. They thought it was wool which grew on a tree instead of a sheep’s back. No other plant is of such value to man as cotton. We should learn something about a plant that is used by man in so many ways as cotton.

The cotton plant of our Southern States is a small shrub-like annual about four feet high. The flowers of the cotton plant are white at first but change to cream color and then are tinged with red. This change takes place over a period of four days when the petals drop off and leave what is called a “boll” in the calyx of the flower. This boll, which is to contain the cotton, is really the seed container of the cotton plant and keeps on growing larger until it is about as big as a hen’s egg. When it is fully grown or ripe the boll cracks and the seeds and fibrous lint burst forth. The bolls are then gathered and taken to a cotton gin, where the seeds are separated from the lint and the lint prepared for weaving.

The boll is divided into from three to five sections. Each section contains a quantity of lint and seeds. When the boll is fully grown the covering of each of the sections cracks and opens up, revealing the contents. It is just like opening the door of each section and having the contents burst out. When these bolls burst open, there is no more beautiful sight in the world than to look out over a cotton field and see the colored people--the “cotton pickers”--busy at their work picking off the bolls.

When the crop is gathered and ginned, the lint is packed into bales and taken to the cotton mill, where it is made into cloth. One of the most interesting industrial processes in the world is to see the bale of cotton go into a cotton mill and come out a piece of cotton goods.

BALES OF COTTON AT COTTON MILL]

The bales are opened, and the cotton is thrown into the large hoppers at the front of these machines, which open and loosen the fibers, work out lumps and remove the grosser impurities, such as dirt, leaf, seed and trash. A strong air draft carries off the dust and foreign particles, and lifts the cotton through trunks to the floor above.]

In these machines, known as Breaker and Finisher Lappers, more of the trash and impurities is beaten out of the cotton, and the lint is carried forward and wound into rolls of cotton batting, known as laps. Several of these are doubled and drawn into one so as to get the weight of each yard as uniform as possible.]

CARD ROOM.

In these machines, known as Revolving Flat Top Cards, the cotton passes over revolving cylinders clothed with wire teeth, and the fibers are combed out and laid parallel with each other. They are delivered at the front of the machine as a filmy web, which is gathered together and formed into a soft downy ribbon or rope, known as card sliver. This is automatically coiled and delivered into cans.]

To insure uniformity in weight, so that the yarn when spun shall run even, the card slivers are doubled and drawn out, redoubled and again drawn out, somewhat in the manner of a candy maker pulling taffy, only here the process is continuous. Six strands of the card sliver are fed in together at the back of the drawing frames, pulled out and delivered as one; and the process repeated. This produces a sliver more uniform in weight, and in which the fibres are more parallel.]

The sliver from the drawing frames is taken to machines called slubbers, where again the fibers are drawn out, and the strand of cotton, now much finer and known as slubber roving, is given a bit of twist to hold it together, and is wound on large bobbins.]

SPEEDERS.

The large bobbins of roving from the slubbers are taken to other machines known as Speeders, and are unwound through the machine, again drawn out finer and finer, and rewound on smaller bobbins. The strand of cotton known as speeder roving is now ready to be taken to the spinning room for the final draft and twist necessary to turn it into yarn.]

The roving from the speeders is placed on the Spinning Frames, and now undergoes its final draft as it passes through the spinning rolls. The attenuated fibres are then twisted firmly together by the action of the spindles, which turn at a speed of about 10,000 revolutions per minute. The yarn thus formed is wound on bobbins and is ready to be dyed and weaved.]

SPOOLERS.

Two kinds of yarn are delivered at the spinning frames, known as warp and filling, which make respectively the lengthwise and crosswise threads of the cloth. The filling is in its completed form ready for the loom; the warp must first be gotten into shape for dyeing and then arranged in parallel rows or sheets of thread for weaving. The first of these processes is spooling, and consists simply in unwinding the yarn from the small bobbins on which it is spun, and rewinding it on large spools.]

The spools of warp yarn are placed in large wooden racks or creels from which they can conveniently unwind. The separate threads are drawn through little wires in the warpers, and are gathered into a bunch or rope of threads, which is wound in a large cylindrical ball known as a warp. If any thread breaks while passing through the warper, the little wire drops and stops the machine. In this way full count of threads and uniform weight of the goods is insured.]

Here the warps, after being boiled and softened to enable the dye to penetrate, are passed through the indigo vats. Several runs are made to get the beautiful depth of color. This Dye-house is equipped with one hundred indigo vats, and is one of the best-lighted and cleanest-kept dye-houses in the world.]

BEAMING FRAMES.

After being dyed, the warps are washed and then passed through drying machinery, from which they are delivered in coils. These are brought to the beaming frames, where they are again spread out into sheets of parallel threads, and passed through the teeth of a steel comb, which separates the threads and prevents tangling, and in this form they are wound on huge iron spools known as slasher beams.]

From the beaming frames the warps are taken to machines known as Slashers, where they are sized or stiffened to enable them to stand the chafing at the looms incidental to the process of weaving. The slasher beams are placed in an iron frame at the back of the slashers and unwound together through the machine. With them some additional threads of white yarn are unwound at either side to form the selvage of the cloth.]

The sheet of warp threads unwinds from the loom beam, receives the filling threads and is wound into a roll of cloth at the front of the loom. This weave room contains 2000 looms. It is 904 feet long by 180 feet wide (about four acres) and is the largest single weave room in the world. Overhead is the roof, which forms one vast sky-light, being of what is known as saw-tooth construction. The vertical sides of the teeth all face due north and are formed of ribbed glass, which affords the most perfect light to every section of the room.]

INSPECTING TABLES.

Before going to the baling presses every yard of cotton cloth passes under the vigilant eyes of the cloth inspectors, who mark as seconds and lay aside all pieces containing imperfections. This inspection is not a mere formality, but is conducted most carefully, and this department is specially located to get the best and most perfect light.]

The bolts of finished cloth are now placed in presses and made into bales of finished cloth and are ready for the market.]

Pictures herewith by courtesy of White Oak Mills.

Who Discovered Cotton?

Just who discovered cotton is not known. The early records are so incomplete that no individual can be credited with the discovery of the value of this wonderful plant. Long before Cæsar’s time, among the Hindoos they had a law that if you stole a piece of cotton you were fined three times its value. Most of the early nations were familiar with cotton--the early Egyptians, Chinese and other ancient people used it and valued it.

What Nation Produces the Most Cotton?

The United States is the leader in the production of cotton, as in many other important world products. We produce more than seventy-five per cent of all the cotton grown in the world. The remainder is practically all grown by East India, Egypt and Brazil.

What is Cotton Used For?

The cotton plant is one of the wonder plants of the world, when you stop to think how well we could get along without wool or silk or other fabrics if we had to.

Little would be lost to the world so far as actual comfort is concerned if all of the other fabric-making materials were lost. We would sleep, as we often do now, in beds the coverings of which were pure cotton, in a room in which the rugs were woven from cotton, the sun kept out of the room by cotton window shades. We could still have plenty of good soap to wash our bodies and clothing, for much of our soap to-day is made from cotton-seed oil; then we could use a cotton towel to dry ourselves; and put on a complete outfit of clothing made entirely of cotton. White cotton table cloths and napkins are not so fine as linen; they are good enough for anyone. Your breakfast rolls will taste quite as well if baked with cottolene instead of lard; the meat for your dinner would be fed and fattened on cotton-seed meal and hulls as they are now; you would have butter made from cotton-seed that compares favorably with the butter you now have on the table; the tobacco in your cigar would continue to be grown under cotton cloth and packed in cotton bags; armies would still sleep under cotton tents and could use gun-cotton to destroy the enemy.

What Are the Principal Cotton Cloths?

There are a great many different names given to cotton cloths, but they may in general be divided into five classes--plain goods, twills, sateen, fancy cloth and jacquard fabrics. The cotton cloth in each of these classes varies and goes by different names. For instance, in Plain Goods, the different kinds are lawn, nainsook, sheeting, mull, print cloth, madras. The difference lies in the number of threads in one inch of width, the fineness and the weave. The Twills have lines running diagonally and are used for linings mostly. The difference is in the weaving. Denim, largely used for overalls, belongs to the class of Twills. Sateen is used for dress linings, dresses and waists. Then there is the class of Fancy Cloths which is another kind of weave used largely in children’s clothes, shirt waists, etc., and under the name Scrim is fine for draperies and towelling. The other class, Jacquard Fabrics, represents the most complicated form of weaving and used largely under special individual names or brands for dress goods, novelties, etc.

How Much Cotton Cloth Will a Pound of Cotton Make?

When the cotton is spun into yarn it is no longer sold by the bale, but by the pound. It is impossible to make an exact statement of the amount of cotton cloth one pound of cotton yarn will make, because of the difference in weaving. It has, however, been figured out that a pound of cotton yarn should make

3¹⁄₂ yards of sheeting, or
3³⁄₄ yards of muslin, or
9¹⁄₂ yards of lawn, or
7¹⁄₂ yards of calico, or
5¹⁄₂ yards of gingham, or
57 spools of thread.

Picture by courtesy Browne & Howell Co.

CHRISTOFORI PIANO FROM THE METROPOLITAN MUSEUM OF ART, NEW YORK CITY.]

The Story in a Piano

What is Music?

Music is one kind of sound. All sounds, whether musical or not, are the result of sound waves in the air. They travel almost exactly like the waves of the water. They go in circles in all directions at the same speed and will go on forever unless they meet something that has the ability to stop them. If you drop a pebble into the exact center of a basin of water, you will see the ring of waves produced start from the point where the pebble entered the water and travel to the sides of the vessel, which stop them. Also the pebble as it falls into the water will make ring after ring of waves.

When you shout or ring or strike one of the keys of the piano you start a sound wave or a series of them, which you can hear as soon as the sound wave strikes your ear. When the series of waves is regular the sound produced is a musical sound, and when the sound waves are not regular in length we call it some other kind of a sound.

Acting on the knowledge so learned, man has devised numerous instruments with which he can produce musical sounds, such as the piano, phonograph, and many others.

Who Made the First Piano?

The first real piano was made by Bartolomeo Christofori, an Italian. He invented the little hammers by the aid of which the strings are struck, giving a clear tone instead of the scratching sound which all the previous instruments produced. It took two thousand years to discover the value of the little hammers in making clearer notes. His first piano was made in 1709. The word by which we call the instrument pianoforte has, however, been traced back as far as 1598, when it is said to have been originated by an Italian named Paliarino. The first piano made in America was produced by John Behnud, in Philadelphia, in 1775.

How Was the Piano Discovered?

~THE DISCOVERY OF STRINGED MUSICAL INSTRUMENTS~

The piano is a stringed musical instrument. The name pianoforte comes from two Italian words meaning _soft_ and _loud_, and is accurately descriptive of the piano because the notes can at will be made soft or loud. The piano is a development of the simplest form of making regular sound vibrations by snapping or hammering a string of some kind which is stretched tight and fastened at both ends. We must go far back into history to find the earliest traces of stringed instruments, and even then we do not know where and when they originated, for there seem to be no records which help us to trace their origin. We know that the Egyptians as far back as 525 B.C. had stringed instruments, but we only know they had them--not where they got them or who made them. There is a legend that the Roman god Mercury, while walking along the Nile after the river had overflowed its banks and the land had again become dry, stubbed his toe on the shell of a dead tortoise. He picked it up to cast it aside and accidentally touched some strings of sinew with his finger. These strings were only what remained of the once live tortoise. At the same time Mercury heard a musical note and, after vainly trying to find a cause for the musical sound, twanged the string again and discovered the music in tightly-stretched strings. He set about making an instrument, using the tortoise shell for the sound box and stretching a number of strings of sinew across it. This is only a legend, of course, but if we examine the early musical instruments of the Greeks, which was the lyre, we always find the representation of a tortoise upon it.

Other nations, such as the early Chinese, the Persians, the Hindus and the Hebrews, had stringed instruments much resembling the lyre. In the tombs of the great rulers of Egypt are found representations of harps, and one harp which had been buried in one of the tombs for more than 3000 years was actually found to be in good condition.

DULCIMER.]

Wherever we search among the records of early nations we find evidence that they were familiar with the music obtainable from playing upon stringed instruments, but we have never been able to discover what people or what persons first learned that music could be produced with such instruments.

~THE FIRST STRINGED MUSICAL INSTRUMENT~

The harp was probably the first practical stringed instrument. Its music was produced by picking the strings with the fingers or with a piece of bone or metal.

The next step was the psaltery, which was produced in the Middle Ages. It was a box with strings stretched across it and represented the first crude attempt at using a sounding board. A larger instrument which came about the same time and was very like the psaltery, was the dulcimer. Both were played by picking the strings with the finger or a small piece of bone or other substance.

Then came the keyboard, first used on stringed instruments in what is called the _clavicytherium_. This consisted of a box with cat-gut strings ranged in a semitriangle. On the end of each key was a quill, which picked the string when the key was operated.

After this came the clavichord. It was built like a small square piano without legs. The strings were made of brass and on the end of each key was a wedge-shaped piece of brass which picked the strings. The elder Bach composed his music on the clavichord, his favorite instrument, and that is why the music written by Bach is full of soft and melancholy notes. The clavichord produced only such notes.

The next steps brought the virginal, spinet and harpsichord. The strings on all three were of brass with quills at the key ends for picking the strings. The virginal and spinet were very much alike. The harpsichord was larger and sometimes was made with two keyboards. These instruments had notes covering four octaves only.

CLAVICHORD.]

The arrangement of the strings in the harpsichord provided one step nearer to our piano. It had five octaves of notes and there were at least two strings to each note instead of only one, as in previous instruments.

SPINET.]

Why Do We Have Only Seven Octaves On a Piano? Why Not Twelve or More Octaves?

Ordinarily the longest key-board of the piano has seven octaves and three notes in addition, or 52 notes, not counting the sharps and flats. An octave you, of course, know consists of the seven notes C D E F G A B. Every eighth note is a repetition of the one seven notes below or above. The reason that there are no more notes or octaves on the piano is that if we extended the key-board either way one or two octaves more, we should not be able to hear the notes struck on the keys. There would be sound produced, or course, but the vibrations would be too fine for the human ear to hear. It is said that the range of the human ear does not go beyond somewhere between eleven and twelve octaves.

UPRIGHT HARPSICHORD.

(From the Metropolitan Museum of Art, New York City.)]

Picture by courtesy Browne & Howell Co.

QUEEN ELIZABETH’S VIRGINAL.]

Photo by Kohler & Campbell Piano Co.

PUTTING ON THE SOUNDING BOARD.

The first operation in producing the piano is to make a wooden frame or back on which is attached first the sounding board, then the iron, harp-shaped frame to which the strings are fastened.

The tones of the piano are produced by felt-covered hammers striking the strings. The sounding board, which is made of wood, magnifies the tones.

This picture shows the mechanics glueing the sounding board to the back.]

Photo by Kohler & Campbell Piano Co.

FASTENING THE STRINGS.

The strings are hitched on to pins in the iron frame at its lower end and fastened at the upper end by a metal pin or peg driven into the back. The peg is square on top, so that it can be turned with a tuning hammer or wrench in order to tighten or slacken the strings, which is the operation of tuning the piano.]

Photo by Kohler & Campbell Piano Co.

BUILDING THE CASE AROUND THE SOUNDING BOARD.

As soon as the sounding board with its iron frame and strings is complete, the outside case is built up around it, the front being left open to receive the action and key-board.]

Photo by Kohler & Campbell Piano Co.

ATTACHING THE LITTLE HAMMERS THAT STRIKE THE STRINGS.

In this picture the workmen are placing the action and keys, to which are attached the little wooden felt-covered hammers, which will strike the strings and produce the tones. It took a great many years for our musical instrument makers to hit upon the idea of using these little hammers, and thus make the piano a perfect instrument.]

Photo by Kohler & Campbell Piano Co.

REGULATING THE ACTION AND KEYBOARD.

This picture shows the piano partly assembled and the workmen adjusting each little black and white key to the proper touch.]

Photo by Kohler & Campbell Piano Co.

TUNING, POLISHING AND FINISHING.

The piano is now complete except for polishing and tuning. The tuning is left to the last. The tuner must have a good ear for music. With his key he tightens or loosens each of the pegs to which the wires are attached until it is perfectly in tune and all in harmony. The piano is now ready to play upon.]

How Sounds Are Produced.

If you look closely at a tuning fork, or a piano string, while it is sounding, you can see that it is swinging rapidly to and fro, or vibrating. Touch it with your finger and thus stop its vibration and it no longer produces sound. The only difference that you can discover in the fork or string when sounding and when silent is that when you stop the motion it is silent and when it vibrates it makes a sound. From this we learn that the sounds are due to the vibrations of sounding bodies. This has been proven by the examination of so many sounding bodies that we believe that all sounds are produced by vibrations.

The question that next presents itself is, how the vibrations affect our ears, so as to produce the sensation of hearing. This may be made clear by a very simple, but striking, experiment. If a bell which has been arranged to be rung by clock-work is suspended under the receiver of an air pump, and the air pumped out, the sound of the bell will grow faint as the quantity of air in the receiver decreases, and finally will stop completely. By looking through the glass of the receiver, however, the bell may be seen ringing as vigorously as at first. We learn thus that the air around a sounding body plays an important part in the transmission of the vibrations to our ears. The way in which the air acts in transmitting the vibrations is as follows. At each vibration of the sounding body, it compresses, to a certain degree, a layer of air in front of it. This layer, however, does not remain compressed, for air is very elastic, and the compressed air soon expands, and in doing so compresses a layer of air just beyond it. This layer expands in its turn, and compresses another layer still further from the body. In this way waves of compression are sent through the air, at each vibration, in all directions from the vibrating body.

It must not be thought that particles of air travel all the way from the vibrating body to the ear when a sound is heard. Each particle of air travels a very short distance, never any further than the vibrating body moves in making a vibration, and the movement of the air particles is a vibratory one, like that of the sounding body. But the particles of air near the sounding body communicate their vibrations to other particles, further from that body, and these, in turn, to others still further away, so, while the particles of air themselves move very short distances, the waves produced by their vibrations may be made to travel a considerable distance.

The size of a sound wave ordinarily is very small, but sound waves are sometimes made of such size and strength as to strike our ears with a force sufficient to rupture the ear drum. Such large and forceful waves come during explosions, such as the discharges of cannon or the explosions of large quantities of gunpowder under any conditions.

What Is Sound?

From what has already been said, you will probably answer that sounds are waves in the air, which produce the sensation of hearing. This is correct, but sound is not limited to vibrations of the air. Other elastic substances can be made to vibrate in the same way, and the waves so produced when conveyed to our ears, produce the sensation of hearing. If you put your ear under water and then strike two stones together in the water you will hear a sound as readily as you would in air. Sound waves may be transmitted by solid bodies also, and some of these are better for this purpose than air or liquids. Perhaps you have tried the experiment of placing your ear against one of the steel rails on a railroad track to listen for the coming of a distant train. If you have tried this, you know that a sound that is too faint, or is made too far away, to be heard through the air, can easily be heard through the rail.

In view of the fact that other substances than air can be thrown into waves that will affect the sense of hearing, we may define sound as vibrations in any elastic object, that produces the sensation of hearing.

The definition is sometimes called the physical definition of sound, in contradistinction to the physiological definition of sound which is given as the sensation produced when vibrations in elastic substances are conveyed to our ears. You will see then that sound when referring to the physical definition is what makes sound known in the physiological definition. The term sound alone, without qualifications, may have either meaning, and therefore statements concerning sound may be misleading, unless we are exact in explaining the sense in which the word is used.

How Fast Does Sound Travel?

When a sound is made close to us, it reaches our ears so quickly that it seems as though it took no time to travel; but when a gun is fired by a person at a distance, you will notice that after you see the flash of the gun, a little time elapses before the sound reaches your ear. It takes a little time for the light from the flash to get to your eyes, but a very short time, which you cannot appreciate. Sound travels much more slowly and the time it takes to travel a few hundred yards is noticeable. Accurate measurements of the speed of sound have been made, and it has been found that sound usually travels in air at a speed of about eleven hundred feet a second. The speed is not always the same, however, for a number of circumstances may cause it to vary. In air which is heated, the speed at which sound travels in it is increased because hot air expands. At the freezing point, sound travels through the air at the rate of 1,091 feet a second, and for every increase in temperature of one degree of heat, the speed is increased about thirteen inches a second. Accordingly at 68° F. the speed would be approximately 1,130 feet a second. Sounds also travel faster in moist air than in dry.

In other gases the speed of sound transmission may be greater or less than in air. For example, in hydrogen gas, which is much lighter than air, sound travels nearly four times as fast as it does in air. On the other hand, in carbonic acid gas, which is heavier than air, sound is transmitted more slowly.

In liquids, which are always heavier than air, you would naturally think that sound would travel more slowly than in air, but this is not true. Liquids are less compressible than gases and this causes the speed with which sound is transmitted in them to be increased. In water sound travels about four times as fast as in air.

What Are the Properties of Sound?

Sounds differ from each other by the extent to which they possess three qualities, namely; intensity, pitch and quality.

The intensity of any sound that we hear depends upon the size of the waves that reach our ears. The size of a sound wave gradually decreases, as the wave travels from its starting point, consequently the intensity of a sound depends upon the distance from the point at which the sound was produced. We know this from experience and if we think of the matter for a moment we will see why it is so. At the start of a sound wave, only a small quantity of air is affected, but for every inch it travels the quantity of air to which the wave is conveyed becomes larger, and the intensity of the waves must grow correspondingly smaller, just as when a pebble is dropped into water, the ripples produced by it are highest at the point where the pebble struck the water, and grows lower and lower as their circle widens.

It has been found possible to measure the intensity of a sound wave, at different distances from the point from which it started, and from these measurements it has been learned that the decrease in the open air, follows a fixed rule that is stated thus: the intensity of a sound wave at any point is inversely proportional to the square of its distance from its starting point. This rule is called “the law of inverse square,” and it means that if the intensity of a wave be measured at two points, distant say one hundred, and two hundred yards, respectively, from the starting point of the sound, the intensity of the sound at the first point will be found to be four times as great as at the second point.

Why Can You Hear More Easily Through a Speaking Tube?

We have seen that the decrease in intensity of a sound wave as it travels through the air, is due to the fact that the quantity of air set in motion by it is constantly increasing. But, if a wave is conveyed through a tube containing air, the quantity of air to which the vibrations are communicated does not increase as the wave travels forward, and theoretically there is no decrease in intensity. When a wave is actually transmitted in this way, however, it is found that there is some decrease in intensity on account of the friction of the particles of air against the sides of the tube; but the decrease from this cause is much slower than that which occurs in the open air, and consequently sounds can be heard at much greater distances through tubes than through the open air. Tubes for speaking purposes are frequently used to connect different parts of the same building, and if the tubes are not too crooked they serve their purpose very well.

Pitch is that property of sounds that determines whether they are high or low. The pitch of a sound depends upon the number of vibrations a second which the body that produces it makes. The sound of an explosion has no pitch because it makes but one wave in the air. The sound made by a wagon on a pavement has no definite pitch, for it is a mixture of sounds, in which the number of vibrations per second is not the same. Pitch is a property of continuous sounds only, and it is apparent chiefly in musical sounds, by which we mean sounds in which the vibrations are continuous and regular. In music, however, pitch is very important. In a musical instrument, the parts are so arranged that the sounds produced can be given any desired pitch, and it is by controlling the pitch that the pleasing effect of musical sounds in large measure is produced. Sounds of low pitch are produced by bodies making but a few vibrations a second while high-pitched sounds are made by bodies that vibrate rapidly.

Quality, may be defined as that property of sounds which enable us to distinguish the notes produced by different instruments. Two notes, one of which is produced upon a piano, and the other upon a violin, may have the same pitch and be equally loud, yet they are easily distinguishable. The difference in them is due to the presence of what are called overtones.

What Is Meant By the Length of Sound Waves?

The length of a sound wave embraces the distance from the point of greatest compression in one wave to the same point in the next. This depends upon the pitch for if a sounding body is making one hundred vibrations a second, by the time the one hundredth vibration is made, the wave from the first vibration will have travelled about eleven hundred feet from the starting point, and the remaining ninety-eight waves will lie between the first and the one hundredth. In consequence of this, the wave length for that particular sound will be about eleven feet. If the sounding body had made eleven hundred vibrations a second by the time the first wave had travelled eleven hundred feet, there would have been eleven hundred waves produced, and the wave length for that sound would be one foot. The wave lengths of sounds produced by the human voice usually lay between one and eight feet, though some singers have produced notes having wave lengths as great as eighteen feet, and others have reached notes so high that the wave length was only about nine inches.

When a tuning fork is struck, it produces a sound so faint that it can scarcely be heard unless the fork is held near the ear; but if the end of the fork is held on a box or table, the sound rings out loudly and seems to come from the table. The explanation of this is very simple. When only the fork vibrates, it produces very small sound waves, because its prongs are small and cut through the air. But when it is set on a box or table, its vibrations are communicated to the support, and the broader surface of the box or table sets a larger mass of air in vibration, and so amplifies the sound of the fork. When a surface is used in this way to reinforce the vibrations of a small body, and thus produce sound waves of greater volume, it is called a sounding board. Many musical instruments, like the violin and the piano, owe the intensity of their sounds to sounding boards, which reinforce the vibrations of their strings.

~WHAT A SOUNDING BOARD DOES~

Columns of air, like sounding boards, serve to reinforce sound waves. Unlike sounding boards, however, they do not respond equally well to a large number of different sounds. They respond to one sound only, or to several widely different ones. This may be shown as follows: Take a glass tube about sixteen inches long, and two inches in diameter, and after thrusting one end of it into a vessel of water, hold a vibrating tuning fork over the other end. By gradually lowering the tube into the water a point will be reached at which the sound becomes very loud, and as this point is passed the sound gradually dies away again. By raising the tube again the sound is again made loud when the tube reaches a certain point. This shows that to reinforce sound waves of a certain vibration frequency, the column of air in the tube must be of certain length.

Let us now see why the waves produced by the tuning fork are reinforced only by a column of air of a certain length. When the prongs of the fork make a vibration, a wave of air is produced which enters the tube, goes down to the water, is reflected, and comes back toward the fork. Now, if the reflected wave reaches the fork at the precise moment when it has completed one-half of its vibration and is about to begin upon the second half, it will strengthen the wave produced by the second half of the vibration; but if the reflected wave reaches the fork before or after the beginning of the second half of the vibration, it will not reinforce it. At the downward movement of the lower prong of the tuning fork, a wave of compression is sent down into the tube, and is reflected at the surface of the water. In order to reinforce the wave produced by the prong when it moves upward, the reflected wave must reach the fork just at the time that the prong reaches its normal position and before it starts upon the second half of its vibration.

Not only do columns of air tend to reinforce notes having a certain rate of vibration, but all elastic bodies have a certain rate at which they tend to vibrate, and when sounds having the same rate of vibration are produced near them, these bodies will vibrate in sympathy with them. If the sounds be kept up long enough, the sympathetic vibrations in objects near them sometimes become so great that they can easily be seen. Goblets and tumblers made of thin glass show this property very strikingly. When the proper notes are sounded the glasses take up the vibrations, and give a sound of the same pitch. If the note is loud, and is continued for some time, the vibrations of a glass sometimes become so great that the glass breaks. Large buildings, and bridges also, have rates at which they tend to vibrate, and this fact is the foundation for the old saying, that a man may fiddle a bridge down, if he fiddles long enough.

Musical Instruments.

By musical sounds, are meant sounds that are pleasant to hear, and their combination in such a way that their effect is agreeable produces music. Any instrument, therefore, that is capable of producing pleasing sounds may be called a musical instrument, and music is sometimes produced by very odd devices; but by musical instruments we ordinarily mean instruments that are especially designed to produce musical sounds. The number of such instruments that have been invented is enormous, but all of them may be divided into comparatively few classes, only two of which are of much importance. The two classes, only two of which are of much importance. The two classes referred to are stringed instruments and wind instruments.

~WHAT PITCH IS IN MUSIC~

Stringed musical instruments are those in which the sounds are produced by the vibration of a number of strings, and are generally reinforced by a sounding board. The strings are arranged in the instruments in such a way that the pitch of the sound produced by each string shall bear relation to the pitch of those obtained from the other strings. As long as this relation exists, the instrument is said to be in tune, and when the relation is destroyed, the instrument is out of tune, and the music produced by it is apt to contain what we call discords.

The conditions that determine the pitch of sounds produced by strings can be very easily discovered by experiment. Thus, by taking two pieces of the same wire, one twice as long as the other, and stretching them equally, you will observe on striking them that the shorter one yields the higher note. If their vibration frequencies are measured it will be found that the shorter string has a vibration frequency just twice as great as that of the longer string. From this we conclude that when two strings of the same size (and material) are stretched equally taut, their vibration frequencies are inversely proportional to their lengths.

By now taking two pieces of wire, of the same size and length, and stretching them so that the tension of one is four times as great as that of the other, we shall find that the vibration frequency of the tighter string is just twice as great as that of the looser. Thus, we see that the vibration frequency depends upon the tension applied to a string, and, that in strings of the same size and length, the vibration frequencies are proportional to the square roots of their tensions.

Now taking two strings of the same length, but with the diameter of one twice as great as that of the other, and stretching them equally, we shall find that the vibration frequency of the smaller string is twice that of the larger; which shows that when the lengths and tensions of two strings are equal, their vibration frequencies are inversely proportional to their diameters.

In constructing stringed instruments, advantage is taken of each of these conditions that affect the vibration of strings, and the requisite pitch is secured in a string by choosing one of convenient length and diameter, and by stretching it to just the right tension.

When a string is plucked in the middle, it vibrates as a whole, and its rate of vibration, or vibration frequency, is determined by the three conditions that have just been discussed; but if a finger is laid on the string, in the middle, and the string is plucked between the middle and the end, the string will vibrate in halves, and the middle point will remain at rest. If the string had been touched at a point one-fourth of the length from the end it would have vibrated in fourths, and there would have been three stationary points.

When vibrations are set up in a string, with nothing to prevent the free vibration of the whole string, it first vibrates as a whole, and the sound produced is known as the fundamental tone of the string; but very soon smaller vibrations of segments of the string begin, first of halves of the string, then of thirds, and then of fourths. These smaller vibrations produce sound waves that blend with the fundamental tone and are known as overtones. The combined sound of the fundamental tone and the overtones is called a note. The overtones present in notes that have the same fundamental tone are not the same when the notes are produced by different instruments, and, consequently, the sound of notes of the same pitch is not the same on different instruments. This difference in notes of the same pitch has already been mentioned, but the way in which overtones are produced was not explained in connection with it.

In wind instruments the sounds are produced by the vibrations of columns of air in pipes. In the organ, which is probably the best example of a wind instrument, the vibrations are usually produced by causing a current of air to strike a sharp edge, just above the opening of the pipe, as is done in a common whistle. A portion of the air current is deflected into the organ pipe, and it sets up vibrations in the air within the pipe.

The pitch of the sound produced by an organ pipe is determined by the length of the pipe. A pipe that is open at both ends, called an open pipe, produces a sound that has a wave length twice as great as the length of the pipe; and if the pipe is open at one end only, a closed pipe, the sound produced has a wave length twice the length of the open pipe. Hence it will be seen that a closed pipe produces a sound that has the same pitch as that produced by an open pipe that is twice as long.

Talking Machines.

The phonograph, graphophone, gramophone, sonophone, and other talking machines, furnish one of the best proofs of the wave theory of sound, because their invention was based upon that theory. The first talking machine was that invented by Thomas A. Edison and called by him the phonograph. The others merely show the principle of the phonograph applied in different ways, and need not be separately described. The reasoning that led Edison to invent the phonograph was that if the sound waves produced by the human voice were allowed to strike a thick disk of hard rubber or metal, they would cause the disk to vibrate in a certain way, and if the disk were again made to vibrate as it had done under the influence of the voice, the sounds of the voice would be reproduced. The difficult part of the task of making a talking machine was in finding a way to make the disk vibrate again as it did under the influence of the voice. This, however, was finally accomplished, providing the disk with a needle, that rests on a cylinder of hard wax, which turns slowly under the point of the needle while the sound waves are striking the disk. The vibrations of the disk cause the point to indent the surface of the wax so as to produce a groove of varying depth on its surface. After the vibrations of the speaker’s voice have been recorded in this way on the surface of the wax cylinder the needle can be made to retrace its path, and will cause the disk to vibrate as it did under the tones of the speaker’s voice. These last vibrations of the disk produce sound waves similar to those of the voice, but their amplitude is less and the sound is not so loud.

Why Does Red Make a Bull Angry?

It is very doubtful if a red flag really makes a bull more excited or more quickly than a rag of any other color or any other object which the bull can see plainly but does not understand. Conceding for the moment that red excites a bull more than any other color, the answer to the question will be found in the statement that anything unusual which the bull sees has a tendency to make him angry and the thing which he can see at a distance more quickly will start him going most quickly. He can see a red rag better perhaps than almost any other color. There may be something about the color which excites him just as some notes on the piano will worry some dogs, but there is no way of studying the bull’s anatomy to determine why red should excite him more than any other color, if that is so.

HOW A KEY TURNS A LOCK

What Happens When the Knob is Turned?

All of that portion of the lock which is shown above the round central post is operated by the knob, the spindle of which passes through the square hole. Before the knob is turned, the parts are in the position shown in figure 2, with the latch bolt protruding. Turning the knob to the left gives the position shown in figure 1, the upper lever in the hub pushing back the yoke, which in turn pushes back the latch bolt. When the hand is removed, the springs cause the parts to return to the position shown in figure 2. Turning the knob to the right also retracts the latch bolt, as shown in figure 3, by means of the lower lever on the hub.

The spiral spring on the latch bolt is lighter than the one above it. This gives an easy, lively action to the bolt, with very little friction when the door is closed, while the heavier spring above gives a quick and positive action of the knobs.

What Happens When the Key is Turned?

All of that portion of the lock which is shown below the round central post is operated by the key. The square stud is attached to the bolt, and in figure 1, it is seen that the projections on the flat tumblers prevent the stud from moving forward, holding the bolt in retracted position. When the key is turned as shown in figure 2, it raises the tumblers releasing the stud, and then pushes the bolt out, the tumblers falling into position as shown in figure 3, with the projections again engaging the stud and preventing the bolt from moving until the key is turned backward, again raising the tumblers and releasing and retracting the bolt.

How Key Changes Are Provided.

There are three ways in which keys are made individual to the locks they fit.

_a._ By changing the shape of the keyhole. This may be done shorter or longer, wide or narrow, straight or tapering and with projections on the sides which the key must fit, making it difficult or impossible for keys of a different class to enter the lock. In the lock shown, a projection on the keyhole will be noted, fitting a groove in the bit of the key.