woodwind instrument: see wind instrument.

wind instrument, in music, any instrument whose tone is produced by a vibrating column of air. In the pipe organ the column of air is set into vibration by mechanical means. Other wind instruments are blown by the player and are divided into two groups, the woodwinds and the brass winds, or brasses. The woodwinds include the flute family, played without a reed, the clarinet family, having single-reed mouthpieces, and the oboe family, having double-reed mouthpieces (see reed instrument). The brass winds include the bugle, cornet, ophicleide, trombone, trumpet, and tuba, all having cup-shaped mouthpieces, and the French horn, having a funnel-shaped mouthpiece. In the brasses the lips of the player perform the function of reeds. The wind passage of a wind instrument is called the bore and may be conical or cylindrical; its flared edge is called the bell. Woodwind and brass instruments are now best distinguished according to their mouthpieces, since metal flutes and saxophones remain woodwinds regardless of the material used to make them.

transposing instrument, a musical instrument whose part in a score is written at a different pitch than that actually sounded. Such an instrument is usually referred to by the keynote of its natural scale—the clarinet in A, for example—in which case A is sounded when the tone C appears in the musical notation. Since A is a minor third below C, the part for this instrument must be written a minor third higher than it is to sound. Transposing instruments were necessary in the 17th and 18th cent. when the natural brasses and the clarinets could be played easily in only a few keys; they were therefore built in specific keys. Although improved construction in the 19th cent. obviated this necessity, all clarinets, the English horn, oboe, French horn, trumpet, alto flute, cornet, and most saxophones are transposing instruments. Parts for the piccolo, double bass, and contrabassoon are written an octave below or above actual pitch to avoid ledger lines, but this is not, strictly speaking, transposition.

transit instrument or transit, telescope devised to observe stars as they cross the meridian and used for determining time. Its viewing tube swings on a rigid horizontal axis restricting its movements to the arc of the meridian. In the field of view of the eyepiece are threads of spider web or fine lines ruled on thin glass. The threads or lines are parallel in a north-south direction and odd in number. Precise adjustment places the middle line exactly on the meridian. After the observer has noted the times at which each line is passed by the star, he averages them to learn the instant at which the star was on the meridian. In modern transits, known as meridian circles or meridian telescopes, the observer merely presses a button as the star crosses each line. Electrical impulses are recorded on a revolving drum at one or two second intervals as they pass through a chronograph. The meridian circle is equipped with precisely graduated circles mounted on the horizontal axis. Stationary verniers, or reading microscopes, mounted on the fixed supports of the telescope enable the observer to read the circles. The meridian telescope gives the altitude of a star as well as the transit time. This information yields the right ascension and declination, i.e., the location of the star in the celestial sphere. The meridian circle has largely replaced the transit as the equipment of observatories, although the older transit instrument is still used to some extent for determining sidereal time. For a discussion of the transit used by engineers, see surveying.

stringed instrument, any musical instrument whose tone is produced by vibrating strings. Those whose strings are plucked with the finger or a plectrum include the balalaika, banjo, guitar, harp, lute, mandolin, zither, the sitar of India and Pakistan, the koto of Japan, and countless others. Those plucked by means of a keyboard include the harpsichord and spinet. Those played with the bow are principally of the viol and violin families, the kemence of Turkey and Central Asia, the rebab of the Arab world and the many varieties of spike fiddle in Indonesia, Central Asia and elsewhere. Instruments whose strings are struck include the dulcimer of Europe and America, the santur of Iran, Iraq and other countries, and several keyboard instruments, among them the piano and clavichord.

reed instrument, in music, an instrument whose sound-producing agent is a thin strip of cane, wood, plastic, or metal that vibrates as air is passed over it. The predecessor of these instruments is the Chinese sheng. Single-reed instruments have one reed that is either free or beating. Free reeds, such as those in the reed organ, accordion, concertina, and harmonica, do not overlap the air passage; they are generally of metal. Beating reeds, such as those used in organ pipes and in the clarinet, strike the edges of the aperture while vibrating. Double-reed instruments, such as the shawm, oboe, bassoon, and English horn, have two reeds facing each other, between which air is forced into the instrument; thus the reeds are set vibrating.

percussion instrument, any instrument that produces musical sound when its surface is struck with an implement (such as a mallet, stick, or disk) or with the hand. Perhaps the most universally familiar percussion instrument is the drum, common to the most primitive as well as the most sophisticated musical arts. Sticks clicked against each other are another simple form of percussion. These are related to castanets, cymbals, and the triangle. Among the percussion instruments used in the West are the bell, the celesta, the glockenspiel, the xylophone (and similar marimba), and the Caribbean steel drum. In general, percussion instruments are not tuned by construction; pitch, tone, and volume depend on the skill of the performer.

See also gong, kettledrum, snare drum, tambourine, and tom-tom.

negotiable instrument, bill of exchange, check, promissory note, or other written contract for payment that may serve as a substitute for money. It is simple in form and easy to transfer. Transfer of a negotiable instrument, accomplished by delivery or endorsement and delivery, gives the new holder of the contract the right to enforce fulfillment in his own name. Negotiable instruments made payable to bearer are transferred by delivery; those made payable to order are transferred by endorsement and delivery. Like commercial paper, negotiable instruments were developed to meet the needs of trade. They are used by businessmen to facilitate long-distance transactions and to avoid the constant exchange of large amounts of cash.

instrument-landing system (ILS), ground-based radio system designed to provide an airplane pilot with precise guidance for the final approach in landing. The pilot flies his aircraft along a course delineated by the intersection of two radio beams—the localizer beam for guidance in the horizontal plane and the glide-slope beam for guidance in the vertical plane. These beams activate an indicator in the aircraft that contains a horizontal needle sensitive to deviations from the glide slope and a vertical needle sensitive to deviations from the localizer path. By keeping both needles centered, the pilot can guide his aircraft down to the end of the landing runway aligned with the runway center line. Limitations inherent in the system prevent it from being used safely in locations where the land beyond the approach end of the runway is not level. Also, false guidance can result from distortion of the radio beam by nearby buildings or mountains. Newer systems using microwave beams overcome most of these limitations. Radio marker beacons are also installed at several locations along the approach path to tell the pilot on the landing approach how far he is from the end of the runway. ILS is an approach rather than a landing system. It is called instrument low approach system (ILAS) by the U.S. military air forces. As a supplementary safety measure, especially in bad weather and for emergency landings, the ground-controlled approach (GCA) system is used. Precision radar indicates the location and movement of an aircraft to the ground controller at an airport, enabling him to direct the pilot by voice radio.

instrument flight regulations: see air navigation.

brass wind instrument: see wind instrument.

Any musical wind instrument that produces sound by either directing a stream of air against the edge of a hole or by making a reed or a double reed vibrate (see reed instrument). In a brass instrument, by contrast, the airstream passes directly from the player's vibrating lips into the air column. The orchestral woodwinds include the flute, piccolo, clarinet, oboe, English horn, and bassoon. Other woodwinds include the saxophone, recorder, panpipe, shakuhachi, and shawm.

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Any musical instrument that produces sound by the vibrations of strings. The strings may be of gut, metal, fibre, or plastic, and may be plucked, bowed, or struck. The orchestral stringed instruments include the violin, viola, cello, double bass, and harp. Keyboard stringed instruments include the clavichord, harpsichord, piano, and virginal. Seealso Aeolian harp; balalaika; dulcimer; guitar; kithara; koto; lute; lyre; mandolin; pipa; sitar; aynūd; ukulele; viol; zither.

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Any musical wind instrument that sounds when the player's breath or air from a wind chamber causes a reed (a thin blade of cane or metal) to vibrate, thereby setting up a sound wave in an enclosed air column or in the open air. Reed pipes have single or double reeds. A double reed, as in the oboe or bassoon, consists of two cane blades tied together that beat against each other. A single reed may hit against a frame (beating reeds), as in the clarinet or saxophone, or it may vibrate freely through a closely fitting frame (free reeds), as in a harmonica or accordion. Beating reeds in woodwind instruments depend on the pipe's sounding length (as determined by the fingering) to determine the pitch. Free reeds have their own single pitch, determined by their thickness and length. Seealso English horn; shawm.

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A musical instrument that is struck (or sometimes shaken or scraped) to produce sound. This category includes instruments whose own hard substance is made to vibrate (idiophones) and instruments that include a tight membrane that vibrates (membranophones). Percussion instruments may produce tones of definite or indefinite pitch. Their primary function is often rhythmic, but many are used as melody instruments. They include the bell, carillon, cymbal, drum, dulcimer, gamelan, glockenspiel, marimba, piano, steel drum, tabla, tambourine, timpani, vibraphone, and xylophone.

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Association of numbers with physical quantities and natural phenomena by comparing an unknown quantity with a known quantity of the same kind. Weights and measures are standard quantities with which such comparisons are made. The earliest ones measured mass (weight), volume (liquid or dry measure), length, and area using units mostly based on dimensions of the human body. The cubit, representing the distance from elbow to fingertips, was the most widespread unit of measure in the ancient world. As such units were standardized, more were added, including units of temperature, luminosity, pressure, and electric current. Measurements made by the senses instead of by measurement devices are called estimates (see estimation).

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Musical wind instrument, usually made of brass or other metal, in which the vibration of the player's lips against a cup- or funnel-shaped mouthpiece causes the initial vibration of an air column. The trumpet, trombone, French horn, tuba, euphonium, sousaphone, cornet, flügelhorn, and bugle, as well as historical instruments such as the ophicleide, cornett, and serpent, are considered brass instruments (though the last two were made of wood); the saxophones, though made of brass, are reed instruments classified as woodwind instruments.

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