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    "source_key": "britannica_1926",
    "source_title": "Encyclopaedia Britannica (1926)",
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    "chunk_id": "1926:phonetics:e23d1cda192f",
    "title": "PHONETICS",
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    "verified_text": "considerable developments have taken place in phonetic science since 1910. the nature of many known speech-sounds has been determined with greater accuracy than before; attention has been given to features of pronun- ciation previously barely touched upon (notably intonation and 1g gr, the theory of phonemes); many new languages have been sub- jected to phonetic analysis; new methods of teaching pronuncia- lion have been evolved, and the use of phonetic methods in practical language teaching has been greatly extended. the organic-acoustic method —the most useful practical method of determining the formation of spcech-sounds is still the ‘ organic-acoustic ’? method, e.¢., estimating the position of the tongue by muscular sensation and by comparison of the acoustic quality of the sound to be analysed with that of other sounds of known tongue positions. this method has been sup- plemented by experimental methods (the use of apparatus, such as the phonetic kymograph, artificial palates and x-ray photog- raphy). for illustrations of the use of the kymograph and artificial palates sce d. jones’s outline of english phonetics (1918 and 1922). x-ray photography was adopted first by e. a. meyer as long ago as 1905,' and has been followed by other aw as saree gg oo ~ = ———————— fig. 4. _ fic. 1.—graphic representation of tongue positions of vowels. fig, 2.—tongue positions of i, e, €, a. fic. 3.—tongue positions of a,3,0,u. fic. 4.—diagram illustrating the nature of the vowcls of italian, by reference to the cardinal vowels. (cardinal vowels shown by black dots; [talian vowels by circles.} investigators. particularly noteworthy are the x-ray photo- graphs taken of the mouths of daniel jones and stephen jones by dr. h. trevelyan george? and a remarkably good set of 30 skiagrams of the mouth of stephen jones taken by h. a. harris and i’. melville in the department of physiology, university college, london, in 1925 (not yet published). e. a. meyer has also obtained valuable results from an ingenious adaptation of the artificial palate.3 the relative tongue-positions of vowels may be indicated graphically by dots placed on a figure of the shape shown in fig. 1. figs. 2 and 3 show the reasons for this. the upper curve from 1 to u in fig. 1 is parallel to the roof of the mouth; the descending part, u-a, indicates the limit of possible vowel- positions of the tongue in the backward direction. the de- scending part, 1-a, of the lower curve indicates the limit of possible vowel-positions of the tongue in the forward direction, while the part, a-a, which is nearly horizontal, represents the lowest positions which the tongue can take up. the highest part of the tongue in pronouncing any vowel may be represented 1 see article by him in medizinisch-pddagogische monaisschrift fiir sprachhetlkunde, nos. 8, 9 (1907). 2 some of these are reproduced in proc. royal institution (1919). 3 see his “ untersuchungen tiber lautbildung ” in festschrift w. vietor (marburg, 1910), and *' beitrage zur schwedischen phonetik \" in vox, part § (1916). 118 by means of a dot placed at the appropriate spot on the cir- cumference or in the interior of this diagram. in practical language teaching, this diagram is generally re- placed by one of the shape shown in fig. 4. the introduction of angles serves to render the placing of the dots more definite and intelligible to ordinary learners, and facilitates the demar- cation of a series of vowels known as “ central ”’ vowels, which are represented by dots placed within the inner triangle shown in fig. 4. this vowel figure, though being by no means mathe- matically accurate, 1s more accurate than its predecessors, the triangular arrangement (adopted by vietor and others), the square (bell and sweet) and the form \\—_/ (passy). the quality of vowel sounds is dependent upon other factors besides the tongue-position. foremost among these are the positions of the lips, which are now generally classified as “spread ” (as for [i]’), “‘ neutral ” (as for [a]), ‘ open rounded ” (as for [9]) and ‘“ close rounded ” (as for [u!). some writers still use sweet’s further classification, based on the muscular condition of the tongue, into “ narrow ” (‘‘ tense ”’) and “f wide ”’ (“ slack,” “lax ”’) vowels. others, however, now consider it better to classify according to the width of the pharyngeal ‘ passage, as this can be more satisfactorily measured than can the degree of tenseness or laxness of the tongue muscles. thus fi] (as in eat) has a wide pharynx; [a] (as in cab) has a narrow pharynx. the cardinal vowels—one of the most important modern developments of phonetics has been the establishing of a system of “cardinal vowels”? as a standard of vowel-quality.. by reference to eight vowels which have been carefully chosen, it is possible to describe the vowel-sounds of any language more accurately than before. their relations to each other are shown by the black dots in fig. 4; it is taken as a convention that nos. 7 and 8 have close lip-rounding, and that no. 6 has open lip- rounding. the old plan of describing vowels by key-words from existing languages has been discarded, since key-words are pro- nounced in a variety of ways by diflerent speakers. the eight primary cardinal vowels were selected as follows: the vowel sound produced with the front of the tongue raised as high as possible towards the hard palate is chosen as cardinal vowel no. 1. it is represented by the symbol [i]. all the i-like sounds occurring in any language or dialect (e¢.g., the different varieties of english [i] in ea, french [i] in ete, windustani [i] in bhi) can be described by reference to this fixed vowel position and the description understood by any reader knowing the value of cardinal vowel no. 1. the vowel sound produced with the tongue held as low and as far back as possible is cardinal vowel no. s, the symbol for which is [a]. english [a] as in calm, french [a] in pas, swedish [a] in glad, have values not fur removed from cardinal [a], and may be accurately described by reference to it. the cardinal vowels nos. 2, 3 and 4, represented by the symbols [el], [el, [a], were chosen so that the distances between successive pairs of cardinal vowels are, from the acoustic point of view, as equal as a highly trained ear can estimate. nos. 6, 7 and 8 [9], fo], fu], are “‘ back ” vowels so chosen as to form a continuation of the acoustic series |i, ¢, €, a, a]. a set of secondary cardinal vowels (phonetically ly, 6, ce, v, e, a, 8, wi) is derived from the primary cardinal vowels by adding lip-rounding to [i, e, e, a, a] and unrounding fo, o, ul. there are also some “ central ” vowels, of which the chief are [1] gntermediate between [i] and [w]),% (intermediate between [y] and [{uj), [o] (the ‘“ neutral” vowel) and [9] (variety of the vowel in bird). the cardinal vowels can only be learnt from a teacher who knews them, or, failing that, from a gramophone record.? by means of dots placed on the cardinal vowel chart, together with instructions as to lip positions, anyone familiar with the cardi- nal vowels can form a good idea of the acoustic effects of forcign vowels, even if he has never heard them pronounced by a 1 letters in square brackets are phonetic symbols (international phonetic system). 2 double-sided record no. b 804 in the catalogue of the gramo- phone co. (363 oxford st., london, w, i.). phonetics native. thus fig. 4 shows the nature of the vowels of italian (shown by circles). phonemes.— another development of far-reaching importance has been the elaboration of the theory of ‘‘ phonemes,” which has placed the distinction between a “broad” and “ narrow ” transcription on a firmer basis. the speech sounds (phones) existing in any one language are much more numerous than the average native speaker of that language imagines. they can be grouped into families technically called ‘ phonemes.” fach phoneme contains the most frequently used member of that family and a number of subsidiary members which take its place in certain positions in connected speech. for example, the sound of [h| in foop is not the same speech-sound as that in he or in aulf. vhese and other varieties of [h] occurring in english belong to the english ‘“ h-phoneme.” in japanese, the h-pho- neme includes such very different sounds as a voiceless palatal fricative [¢] (used before [i]) and a voiceless bilabial fricative lr] (used before [u]). in the speech of most english people, the initial [l| in zitle (“ clear ” 1) is not the same sound as the final {1] (“ dark ’ i). these two ]-sounds, and others with vary- ing degrees of ‘ clearness” and ‘ darkness,’ belong to the english l-phoneme; the particular variety to be used in any given word or phrase depends upon the nature of the surrounding sounds. the a-phonemes in russian and in arabic contain mem- bers differing very widely from each other; the arabic a-phoneme includes vowel-sounds ranging from a sound near to (x) (as in man) to (vp) (as in nof) and (a) (as in cup), the character of neighbouring consonant sounds being responsible for these variations. in french the l-phoneme includes a voiceless (}) which is used when such words as oncle, sinzple occur finally. in connected speech the use of the chief members of phonemes alone would never cause misunderstanding, for they are sufficient to distinguish the meanings of words; the proper use of the sub- sidiary members, though not essential for intelligibility, is never- theless necessary if one wishes to speak a foreign language “like a native.” two different speech-sounds may be members of the same phoneme in one language but belong to different phonemes in another language. thus in welsh and zulu there exists a variety of voiceless ||] (represented by in welsh, #/ in zulu); this sound is a separate phoneme from [i] in these languages, con- trary to the usage in french. la] (as in psalm) and [se] (as in sam) are separate phonemes in english, but they are members of the same phoneme in russian. phonetic transcription.—it is, of course, impossible to assign a symbol to every known speech-sound. an unambiguous repre- sentation of a given language is effected when a distinctive sym- bol is assigned to each phoneme, for it is only by the phonemes of a language that words are distinguished in meaning. a “ broad ”’ system of transcription is now defined as one which provides one leiter per phoneme; such a type of transcription is adequate for most practical purposes. a more elaborate system (“ nar- row’) is often necessary in comparative phonetics and in recording dialects with minute accuracy. narrow forms of trans- cription may also be uscful, in helping to remember the rules governing the use of subsidiary members of phonemes. intonation —the subject of intonation (the rise and fall of voice-pitch) has received much attention since 1910. researches into the sentence intonation of english, french and german have resulted in the discovery that the apparently complex intonations of these languages are reducible to systems consisting of a few simple rules. each language is found to have certain characteristic “tunes”? which undergo modifications under special circumstances, such as the two kinds of emphasis (“ prom- inence ” and ‘ intensity ’’).3 3the first comprehensive work on intonation was h. klinghardt and m. de fourmestraux’s franzesische intonations-tibungen (1911, rev. ed. 1925, eng. ed. 1923); other notable contributors are h. klinghardt and g. klemm cbungen im englischen tonfall (1920); h. e. palmer, english intonation (1922); m. l. barker, handbook of ees intonation (1925); h. klinghardt, deutsche intonation (1926). phonograph valuable research work has been done on the intonation of “tone languages ”’ (pekingese, cantonese, burmese, japanese, punjabi and various african languages). it has been established that in most “‘ tone languages ” the tones of words in connected speech are often different from the tones of the same words when said by themselves; the actual tones used may be grouped into “tonemes,”’ just as phones are grouped into phonemes. it has been found that in bantu and in japanese tones are used not only to distinguish words of entirely different meaning but also to perform grammatical functions such as the distinction be- tween different parts of the same verb. details of some recent investigations will be found in several of the books given in foot- notes to the next paragraph, also in beach ‘ tonetics” in bantu studies (dec. 1924). languages analysed since 19t0.—languages of which a partial or fairly complete phonetic analysis has been made for the first time since 1910 include pckingese,' cantonese,? burmese,? panjabi,? bengali,? sinhalese,* zulu,> yoruba,* yaunde,? and a number of other african languages.* important additions have been made to our knowledge of the phonetic structure of several european languages (including welsh,? russian,® polish?) and the non-european languages, arabic,t° japanese,\" sechuana,? hausa\" and other african languages. the study of these languages has brought to light many new phonetic facts besides tone systems, e.g., the true nature of affricates (such as the numerous sounds represented by ch by english writers on eastern languages), the existence of “ sulcal ”’ sounds (sounds formed with a furrow down the middle of the tonguc), voiced “ implosive ” (suctional) sounds (as in sindhi), and p, t, s, and other sounds with simultaneous glottal stop. increasing use of phonetic methods in practical language teaching. —the use of phonetic methods, with or without the help of a phonetic transcription, is now recognised as essential by the foremost language teachers in many countries, especially in england, germany, scan- dinavia and japan. these methods are now used in a great number of secondary schools in england, chiefly in connection with the teach- ing of french; they are also used in many training colleges for the purpose of enabling the students in training to become efficient teachers of english pronunciation, during the last 14 years several official reports have appeared in which phonctic methods are ad- vocated: board of [education report on the teaching of modern languages, circular 707 (1912); report of a conference on speech training, issued by the london county council (1916); london county council report on the teaching of french in secondary schools (1917); report of the government committiee on the teaching of fnglish in england (1921); report of the government commutiee on modern languages (1918). the necessity for phonetic research in connection with oriental and african languages was emphasised by the report of the government committee (1918), and phonetics has now for some years been included asa subject for candidates for the indian civil service. bibliography.—among recent books dealing with methods of language teaching, in which the use of phonetics is advocated, may be mentioned w. ripman, the early teaching of french (1915); h. fe. palmer, the scientific study and teaching of languages (1917); h. g, atkins and h. l. hutton, the teaching of modern foreign languages (1920). (dee) 1see beach, the phonetic structure of pekingese, not published, but may be seen in the library of the university of london; yuen ren chao, a phonograph course in the chinese national language. 2sce l. e. armstrong, finglish phonetic reader (1923). 3see n. c. chatterji, bengali phonetics (international phonetic association); also bengault phonetic reader, in university of london press series. 4see d. jones and il. s. perera, colloqgutal sinhalese reader (manchester, i9i9g). 5see doke, the phonetics of the zulu language (univ. of the witwatersrand press, johannesburg), and c. meinhof, “ zur lautlchre des zulu” in zeitschrift fur eingeborenen sprachen, vol. 14, part 4 (1924). 6see a. lloyd james, ‘‘ the tones of yoruba,’”’ bull. oriental studies, vol. 3, part i (1924). 7 see m. heepe, jaunde-texte (hamburg, 1919). 8 see publications of the hamburg colonial institute. 9see m. v. ‘frofimov and d. jones, the pronunciation of russian (cambridge, 1923). 10 see gairdner, the phonetics of arabic (oxford univ. press). 11 see o, pletner, ‘ musical accent in japanese morphology,” bull. oriental studies, vol. 3, part 3 (1925). jimbo, ‘‘ the word tone of the standard japanese language,” bull. oriental studies, vol, 3, part 4 (1925). | 119 phonograph (sce 21.467).—the progress which has been made since 1910 in phonographic reproduction of sounds has re- sulted in two chief improvements. first, notes of speech or music, which formerly presented great differences in their degrees of reproducibility, may now be reproduced with such evenness and impartiality that the ear can scarcely detect any difference between the eflectiveness of reproduction of one note and that of another. secondly, the range cf notes which may be effectively reproduced has been extended from about 3} octaves to ap- proximately 53, nearly 13 octaves being added at the lower end of the scale and about 4 octave at the higher end. effects of electrical recording—these improvements were effected chiefly through the substitution, for the former mechan- ical linkage, of an electrical linkage between the diaphragm re- ceiving the initial sound waves and the stylus recording their equivalents on the wax record. this electrical linkage consists of a vacuum tube amplifier and associated circuits, its purpose being to increase the power delivered by the transmitter whose diaphragm receives the initial sound. this increased power is - used for operating the recording stylus. it is, therefore, no jonger necessary to design the receiving diaphragm and the mechanism for driving the recording stylus with a view to their sensitivity; instead, the objective is to ensure that they follow, with maximum faithfulness, the vibrations of the initial sound waves. the above applies to the making of records in large audi- toriums, as well as in the studio. reproduction.—progress has likewise been made in the re- producing of the sound from the records. the vacuum tube amplifier (see amplifiers) may be used also in the linkage be- tween the device operated by the needle following. the grooves of the record and the diaphragm creating the sound waves for the listeners’ ears. the sound may thus, if desirable, be greatly magnified. in the home, however, where this magnification is not necessary, a mechanical reproducing system in which great improvements have also been effected, is sufficient and simpler. amaterial.—another major improvement concerns the material and manufacture of the finished record, whereby the surface noise or “ roar”? has been materially reduced. in some cases this has been effected by laminating the record, the body con- sisting of a cheap, hard material to which adheres paper coated with the high-grade grooved material. result of new methods —by reason of the improved methods of making the records, the artists are now free to perform in a more natural manner than formerly, and at such a distance from the “ pick-up ” device that the normal reverberations from the studio walls may be duplicated in the recorded sound. figs. r and 2 on plate show, respectively, a group of artists recording by the old method and the same group recording by means of the electric process. it will be noticed in fig. 1 that the artists were grouped very closely about the horn. only two of the violins were of standard construction, the rest being of the type known as the “ stroh,” strung in the manner of a violin but so arranged that the bridge vibrates a diaphragm attached to a horn. this horn was directed toward the recording horn, as shown by the player in the foreground. with such an arrange- ment of musicians, it was very difficult to arouse the spontaneous enthusiasm which is necessary for the production of really artistic music. in fig. 2 the musicians are sitting at ease more nearly in their usual arrangement, and all are using the instruments which they would use were they playing at a concert. furthermore, the pick-up device is now sulficiently far away from the orchestra to reccive the sound in much the manner that the ears of a listener in the audience would reccive it. in other words, it picks up the sound after it has been properly blended with the reflections from the walls of the room. it is in this way that the so-called ‘atmosphere ” or “ room-tone ”’ is obtained. effective limiis——the range of effective sound reproduction has now been increased virtually to the limits inherent in the material from which records are made. the limit at the lower end is fixed by the fact that a very low frequency note will cause the recording needle to cut from one groove into an adjacent one 120 (or, in a vertical cut, will penetrate so deeply as to tear the wax instead of cutting away with a clean surface), while, at the upper end, it is fixed by the cuts in the record becoming so fine and sharp that the reproducing needle will not follow them. the increase in effective range of notes recordable by the new process has resulted in the virtual elimination of metallic tones, char- acteristic of the earlier phonographs, and of the muffled quality of higher notes, provided the reproducing machine covers a similar range. the sibilants, also, which failed formerly to make them- selves heard, may now be reproduced naturally. the latter two improvements are due to the accurate recording and reproducing of the higher harmonics, vibration frequencies ( ieasl fic. 1.—the inductance labelled m, represents the mass of the armature which, when acted on by the magnetic field, forms the driving portion of the mechanical system, the condenser c. produces the flexibility of the shaft connecting the armature to the stylus holder; mz represents the mass of the stylus holder and stylus; cy the flexibility of the shaft connecting the stylus holder with the metal piece which fits into the rubber damping element; m3; the mass of this metal piece; and c; and r represent the properties of the damp- ing element. the two condensers shown dotted and unlabelled represent the effect of the magnetic field on the armature and the restoring force of the balancing springs which hold the armature in its central position. up to 6,000 cycles per sec. being successfully recorded, 1.c., about 3 octave above the highest note on the pianoforte. the elimination of metallic sounds is due to accuracy in recording and reproducing low notes and to the impartiality with which the various notes are treated. in the earlier machines, the funda- mentals of the lower notes failed to be reproduced, but the ear of the listener, hearing the higher frequency harmonics of these notes, added the fundamentals, although the result lacked “body ”’ and sounded “ tinny.”” were it not for this constructive faculty of the ear, the older phonographs and loud-speakers would have been useless. with the recently attained accuracy in actually reproducing the fundamentals of tones as low as 1oo — —— = == ==. = = sss ss eee sss sssi li sass sis 23 2s sss ses eet eee. sese s 20 = se ria gad ga om ree, mn a ers a see eee _ sa eee es a ss se ee a eera sees od fe ere br eee sis | ss case acy se ce as saat em ccs om a) so ot se es foes cece cee gay oot ce = ces) (a c = oa ase sas: a a ee eee eee see se qo ee sa) er ea a ee ee oe ee + +09 c02 4 ca—105 | ce 07 7 c0 = sh cet 09 c4 5 ce © un all phonograph cycles per sec. (13 octaves above the lowest note on the piano- forte), the result has gained remarkably in naturalness. recording methods.—fig. 1, a diagrammatic sketch of one of the recording instruments and of the equivalent electric circuit, shows the manner in which the recording needle is controlled in response to the voltage fluctuations set up by the sound- receiving diaphragm. this instrument is a mechanical filter of the low pass type, providing the two undesignated condensers are omitted. in this particular case the filter has three sections and a terminating resistance. in designing mechanical analogues of such a system, the problem presented is threefold: first, that of arranging the parts so that they form repeated filter sections; second, determining the magnitudes of these parts so that the separate sections all have the same characteristics; third, pro- viding the proper resistance termination. the necessity of meeting these three conditions simultaneously probably pre- vented the solution of this problem by cut-and-try (non-scientific) methods. the credit for the use and design of such mechanical analogues for this purpose 1s due in large part to h. c. harrison. such a filter when properly designed will secure a sensitiveness at the various pitches represented by curve a in fig. 2. the actual recorder, however, owing to the presence of the two undesignated condensers shown in fig. 1, has a loss of response at the low pitch end as indicated by curve b (fig. 2). this loss is unfortunately necessary in order to avoid the large amplitudes which accompany the low pitched notes and which would cause the trace on the record to cut from one groove over into its neighbour, systems employed —many early attempts were made to design mechanical transmission systems having a wide fre- quency range in which highly damped single or multi-resonant systems were employed. in these attempts both of the obvious methods of increasing the damping were used, namely, that of adding a resistance to the system and that of increasing the value of the compliance and decreasing mass in such proportion as to maintain the same natural frequency. the results of these two methods are shown in fig. 3. the former reduces the sen- sitivity of the system at the point where it 1s most efficient (curve b as compared with curve a, which represents the re- sponse of the singly resonant system chosen for illustration). the second method increases the response at the points where the system is less sensitive, namely, away from its resonance point (curve c, as compared with curve a). curve d represents the response when a band pass type of system is used whose resist- ance impedance is the same as that of the system shown in curve a. some of the earlier attempts to improve the range of re- production employed multi-resonant systems. the results of the filter theory have shown how these resonances should be co- ordinated so that, when a proper resistance termination is used, high efficiency and cqual sensitivity are obtained over a definite band of frequencies by elimination of response to all frequencies outside the band. with either the electrical or the mechanical o1 o oo oo 500 1000 cycles per second fic. 2.—curve a shows the response, that is, current, in the series branches of a low-pass filter as a function of pitch. curve b shows a calibration of one of the recording instruments, phonograph fic. 1. scene in recording studio, showing the means required with the older phonograph to create the necessary power for marking the record. the artists are grouped closely about the horn, and the weaker instruments (violins) are specially equipped with ampli- fying horns. fic. 2. studio scene, for recording by means of newer devices. the artists, playing naturally, are at a distance from the receiver, which picks up the sound after it has been properly blended with reverberations from the walls of the room, (courtesy of victor talking machine co., camden, n.j., and the amer. inst. of electr, eng.) phonograph case of a repeating filter, each section considered by itself reso- nates at the same frequency, but when combined into a short- circuited filter of # sections there will be » natural frequencies. however, when such a system is terminated with a resistance 20 s ato e r150 mech. ohms «. mz .f gram ------~ s s-¥x/05 dynes/cm. 20 ; = s30 r=/50 mech.ohms oe mm =,5 gram ~ 840) s =20x106 dynes/cm. 5 r=1000 meth.ohms < m=.5 gram an $=20%106byne 100 1000 10,000 frequency fic. 3.—diagram showing response for various values of mechani- cal constants, which equals the nominal characteristic impedance in the trans- mission band, uniform response in the terminating resistance is obtained over the entire band. new phonograph —fig. 4 shows a diagrammatic sketch of the mechanical system of the new phonograph, while fig. 5 shows the equivalent electrical circuit. from these diagrams it is evident which units in the mechanical system correspond to the various electrical parts. as the series flexibilities co, cyand cg have been mace so large that the low frequency cut-off caused by them lies well below the low frequency cut-off of the horn, an inappre- fic. 4.—diagrammatic sketch of the mechanical recording system of the phonograph. ciable error is introduced in using for design purposes formulae of low-pass filters. the two formulae which have been used are as follows :— m1 () m=ye @) frequency of a lumped transmission system in cycles per second, c=shunt compliance per section in centimetres per dynes, m=series mass per section in grammes, z,= value of characteristic impedance over the greater part of the band range. this may be called nominal mid-shunt or mid-series impedance. their actual values in the trans- where f, = cut-off mission band being at any frequency f, mid-series =25a'1 — w - mid- c zo —_———— shunt === © \\ a equations (1) and (2), which form the basis of the design work, contain four variables, f,, c, m and z. it is, therefore, necessary to determine two of them by the physical requirements of the problem, e21 after which the other two can be determined mathematically. the upper cut-off frequency f. was arbitrarily chosen at 5,000 cp. as a compromise between the higher frequencies occurring on the record and the increase in surface noise as the cut-off is raised. the choice of the other arbitrarily set variable came after considerable pre- liminary experimenting, and was fixed by the difficulty of obtaining a diaphragm which is light enough and has a large enough area. hence the effective mass of the diaphragm ms; (figs. 4 and 5) was fixed at 0-186 grammes, which value can be obtained by careful design. the effective area can be made as large as 13 sq. centimetres. design of the horn.—by the proper use of these two formulae with the two arbitrarily set variables it has been possible to determine mathematically the magnitude of the parts comprising the mechanical system. when this design is complete there still pecistece cies om record p constant current type generator: ci ed ---needle point compliance ak chess eee needle arm transformer tr sm q-needle arm mass co|l|~-pivot compliance a}—_{(— ---needle arm compliance c3 compliance of attachment mas eevee point of arm to spider --spider mass ui}-———_{_— ---spider arm compliance ---diaphragm mass ---diaphragm edge compliance --air chamber compliance 0, air chamber transformer 72 el} ---horn impedance lh fig. §.—electric equivalent of the system shown in fig. 4. remains the terminating resistance, zn, of figs. 4 and 5. this is supplied by the horn, which has been made of the logarithmic type. certain general properties of logarithmic horns have been understood for some time. there are two fundamental constants of such a horn—the first is the area of the large end and the second is the rate of taper. the area of the mouth determines the lowest frequency which is radiated satis- factorily. the energy of the frequencies below this is largely reflected if it is permitted to reach the mouth. from the equations given by webster,! it can be shown that all logarithmic horns have a low frequency cut-off which is determined by the rate of taper. if the rate of taper is so proportioned that its resulting cut-off prevents the lower frequencies from reaching the horn mouth, the horn will then radiate all frequencies reaching its mouth and very little reflec- tion will result. it is, therefore, possible to build a horn having no 1 much credit is due to p. b. flanders, who carried out the mathe- matical investigation of these relationships; and to a. l. thuras, who developed a method of checking experimentally the mathe- matical theory, t22 marked fundamental resonance. since the characteristics of the horn are determined by the area of its mouth and by its rate of taper, the length of the horn is determined by the area of the small fic. 6.—scctional view of folded horn. end. this area is determined in turn by the mechanical impedance and effective area of the system which it is terminating. it is scen, therefore, that the length of the horn should not be considered as a fundamental constant. fssion jransm 200 300 400 500600 860 1000 5 —f | | == eens phonograph an interesting feature of the horn which has been built com- mercially is its method of folding. the sketch in fig. 6 shows a shadow picture of the horn. it will be noticed that the sound passage is folded only in its thin direction, which permits the radius of the turns to be small and thereby makes the folding compact. fig. 7 shows the sensitiveness at various pitches of a phonograph designed as described above with a logarithmic horn whose rate of taper and area of mouth opening place the low cut-off at about r15 cycles. it also shows a similar curve for one of the best of the old style phonographs. curve a represents the new machine, while curve b represents the old style machine. with this new equipment, it is easily possible for a listener to receive the full artistic effect of the music which is being repro- duced, and with certain types of music it is no exaggeration to say that he may have the feeling of actually being in the presence of the artist. (see souund.) bipllography.—j. p. maxfield and h. c. harrison, “ methods of high quality recording and reproducing of music and speech based on telephone research,” 7rans., a.t.f.f. (1926); hh. fletcher, ‘‘ physical criterion for determining the pitch of a musi- cal tone,” phys. rev., vol. 23, no. 3 (march 1924); e. c. wente, “ condenser transmitter as a uniformly sensitive instrument for measuring sound [ntensity,” phys. rev., vol. 10 (1917); i. b. crandall, ‘‘ air-damped vibrating systems,” pays. rev., vol. (1 (1918); e. c. wente, ‘ electrostatic transmitter,” phys. rez., vol. ig (1922); w. h. martin and h. fletcher, ‘‘ high quality trans- mission and reproduction of speech and music,” 7rais., a. 7. ee. f., vol. 43, p. 384 (1924); i. w. green and j. p. maxfield, ‘ public address systems,” jrans., a.j. e. f., vol. 43, p. 64 (1923); g. a. campbell, “on loaded lines in telephonic transmission,” phil, mag. (march 1903), and ‘“‘ physical theory of the electric wave filter,” bell systent technical journal (nov. 1922), sce also u.s. patent 1227113 and 1227114; o. j. zobel, ‘‘ transmission charac- teristics of electric wave filters,” bell sysien technical journal (oct. 1924); k. s. johnson, transnitssion circuits for telephonie communication (1925); a. g. webster, ‘‘ acoustical impedance and theory of hornsand phonograph,” proc., nat. acad. of sei. (1919); hanna and slepian, the function and design of ilerns for lond speakers (1924). (he pe aed ss = [aes saat cei | ¢ ce ¢ | ts |e faa es ee 2000 300040005000 frequency fic. 7.—curves showing sensitiveness at various pitches for the old and newer phonograph. curve a represents the performance of the band pass filter type and curve b of the oldstyle machine. photoelectricivty photoelectricity.—hertz noticed in 1887 that an electric discharge passed more easily between two ncighbouring conductors when the negative electrode was illuminated by an electric spark. hallwachs and others demonstrated that an in- sulated metallic conductor loses negative electricity when illum- inated by light of short wave-length. this loss, observable in vacuo as well as in gases, is known as the photoelectric effect. it is proportional to the intensity of the illumination and to the time for which it acts. it varies with the wave-length of the light, ancl for each metal there 1s a wave-length for which the effect 1s produced. for the alkaline metals this critical wave-length 1s in the visible part of the spectrum. towards the close of the roth century sir joseph thomson and lenard showed by exact experiments that negative charges were formed by the emission of electrons, and that the photoelectrons thus projected possessed a relatively small velocity (of the order of 107 cm. per second). curie and sagnac proved a similar phenomenon in the case of rentgen rays. c. t. r. wilson showed later that ionisation in gases through which x-rays pass is really due to the formation of ions within the gaseous medium, by the rapid photo-electrons removed from the molecules under the influence of radiation. a\\\\ electronic emissions can be measured as to: (a) the number of corpuscules emitted per unit of time, and (6) their individual velocities. investigations to determine these values in the case of photoelectrons showed that although the intensity of the exciting radiation affects the number of electrons emitted, their maximum velocity is entirely unaffected (lenard), this latter quantity, or rather the energy of each corpuscule (richardson, hughes, compton), depending solely upon the wave-length of the rays employed, and being a linear function of the frequency of the exciting radiation. this law, the extent and scope of which has been pointed out since 1905 especially by einstein, is bound up with the quantum theory of light (see quantum theory). denoting the frequency of the exciting rays by vy and planck’s constant by kh, the following relation for the energy of the electrons holds:— (1) where the velocity of the photoelectrons is sufficiently great to cause a variation of their mass with kinetic energy to be appreci- able the above relation must be written in the form:— t y= myc? (j= = 4) f vi— pp from the numerical point of view it is convenient to express the electronic energy (4mv? when the velocities are insuflicient to cause the variation of the mass to intervene) in the form ev, where e is the electronic charge and v the difference of potential required to impart the energy to the electron. the electronic charge being constant, it follows that each electronic velocity ts characterised by a definite voltage, and we may write the quan- tum relation (1) in the form:— v7 221345 » where v is expressed in volts and the wave-length x in ang- strem units. consideration of the relation (1) shows that the slope of the straight line representing the relation between the energies of the frequencies, is exactly equal to planck’s constant #, andl moreover the phenomenon must ptesent a threshold when the frequency of the exciting radiation is just sufficient to overcome the work of extraction k. , the minimum frequency of the light required to produce a photoelectric effect proceeds continuously towards the red end of the spectrum as the illuminated body becomes more electro- positive (alkaline metals): it was thus hoped to obtain for each body a critical frequency which would have been of significance. unfortunately, parasitic effects due to contact differences of potential have prevented the exact determination of these constants. g niv® = ve = hv—k. 123 research has given to photoelectric phenomena a significance of increasing importance, since the loss of electrons which may be produced either by corpuscular shocks or by the emergence of radiation is, in reality, the preliminary excitation which condi- tions the emission of spectral rays by the atoms. (serr atom; atomic energy.) in the rutherford-bohr atomic model the electrons are imag- ine as rotating around a nucleus and divided into layers or levels characterised by their energy or emission. when a radiation of high frequency, such as x-rays, strikes an atom, it may com- municate to an electron of the k layer, for example, energy equal to its quantum—that is to say, remove a photoelectron which possesses, on coming out of the atom, kinetic energy equal to the quantum of the incident radiation, diminished by the energy of emission. at the same time, the re-arrangement of the electrons which restores the atom to the normal state will be accompanied by the emission of the spectral series corresponding to the elec- tronic layer involved. in the case of rays of lower frequency (ultra-violet, visible light) the energy absorbed may carry the electron to a level further removed from the nucleus, without extracting it completely (resonance potential); when the quantum absorbed is sufliciently large the electron is expelled as in the case of x-rays (ionisation potential). the study of photoelectric phenomena is simplified when the velocity of the electrons emitted is sufliciently great for them to travel an appreciable distance, thus rendering negligible the con- tact potential differences experienced in the case of solids and liquids. the action of high frequency rays like x-rays is there- fore better known than that of the ultra-violet and visible rays, which can act only upon the superficial electrons of the atom, that is to say those feebly bound electrons which play such an important rele in the phenomena of conduction, cohesion and chemical affinity. at the present day explanations of photoelectric phenomena start from the absorption of light by a rutherford- bohr atom obeying einstein’s law, and the phenomena first studied, the charge of illuminated conductors follow in conse- quence of this principle. the emission of electrons produced by ultra-violet and visible light has been the object of much experimental and theoretical work. o. w. richardson has consiclered the relation between photoelectric and thermionic effects particularly from the theoretical point of view. millikan has studied the influence of the contact potential differences on the emission of electrons when different metals are illuminated in vacuo by ultra-violet rays. ever since the researches of elster and geitel, physicists (in the case of radiations of low frequency) have distinguished between a normal and a selective effect. in the case of the selective effect the intensity of the effects observed depends upon the orientation of the plane of polarisation of the incident hght, so that if the liquid, sodium-potassium alloy for example, is illuminated, the maximum result is obtained when the electric vector vibrates in the plane of incidence. the photoelectric effect is exactly proportional to the intensity of the light received, and this property is utilised in photometry by means of photoelectric cells—the current of which may be amplified at will. they furnish at the present day the most sensitive and precise instruments for measuring very feeble radiation intensities. astronomical physics, in particular, makes great use of them. radiation may produce the ejection of electrons in matter under bombardment by a very different process; a. h. compton has shown that the diffusion of x-rays may be accompanied by an increase of the wave-length (that is to say, a diminution of the quantum associated with the radiation) and at the same time by the emission of a “ recoil electron ”’ whose kinetic energy is ex- actly equal to the loss of quantum suffered by the incident radiation. | by this theory the encounter between an electron and a quantum of light is compared with a ballistic collision in which the energy and momentum are conserved. 124 bibliography.—h. hertz, wiedemann’s annalen der phystk, vol. 31 (1887); w. hallwachs, idid., vol. 33 (1888); j. elster and h. geitel, zbid., vol. 38 (1889); a. l. hughes, photo-electricity (1914); *“* report on photo-clectricity,”’ bull. of national research council, washington (1921); h. s. allen, photo-electricity (1925). high frequency radiation: —h. robinson and w. f. rawlinson, phil. mag., vol. 28 (1914); m. de broglie, jour. de physique et radium, vol. 2 (1921); c. d. ellis, “ the magnetic spectrum of the b-rays excited by y-rays,”’ proc. roy. sec. (a) vol. 99 (1921); a. h. compton, ' secondary radiations produced by x-rays,” bull. national research council, washington, vol. 4 (1922); hf. robinson, proc. roy. soc. (a) vol. to4 (1923); c. t. r. wilson, ¢bid. (1923); ii. robinson, phil. amag., vol. 50 (1925); jean thibaud, “ les spectres gamma caracteristiques et leur effet photo-clectrique,”’ jour, de physique, vol. 6 (1925), sec also these, ed. masson (1925). (de br.) photo-engraving (sce 22.408).—this term is applied properly only to those photomechanical processes of reproducing pictures which print from a relicf plate. this article, however, deals with similar processes which print from flat surface (plano- graphic) and from sunken jines (intaglio). in great britain the term “ process ” is generally employed instead of “ photo- engraving.” essential principles—by sensitising a metal plate and by photographically printing an acid-resist on it, which protects certain areas, and then etching the unprotected parts with acid, a relief, or intaglio, plate is produced, which can be inked and mechanically printed. all photomechanical reproductive proc- esses are based on the fact that pictures are made up of small grains or dots, whether they be of ink, of paint or of photo- graphic emulsion. concentration of these small grains or dots, bringing them closer together, gives, when printed, a solid colour, while distribution or scattering so that the grains are farther apart, gives a tone—a colour not solid, but tending in some degree toward white. therefore, to reproduce solids or tone, it is only necessary to reconstruct a grain or dot formation on a printing plate or on a printing medium, which will transfer printing ink to paper in the same ratio of concentration as that which produced the tones of the original. grain or dot formations differ in the numerous processes. some are irregular as produced by gelatine colloids, resin or bitumen dust, while others are symmetrical, resulting from the ruled cross line half- tone screens. relief or cameo.—relief plates have their printing elements on a plane; the areas between them are sunken. ink is applied to the surfaces by means of a roller and printing is effected by transfer of the ink from the relief areas to the paper. the print- ing elements vary in size, but all print with a uniform intensity. plano or flat.—planographic printing is done from metal, stone, gelatine or other suitable material, on which the image has been formed of a greasy ink. the surrounding areas, com- prising the spaces between the grains or dots, have an affinity for moisture and when so impregnated reject greasy ink, in printing, both water and ink rollers are used. the former keeps the un-inked surfaces damp, so the deposit from the ink roller will adhere only to the image to be printed. the materials used for some classes of planography are impregnated with ink repellents, such as mercury. ‘these require no water roller, the repellent acting in its stead. as with relief plates the printing elements in planography print with uniform intensity, but they vary in size. intaghio or sunken—tintaglio plates have their lines, dots or grains sunken like grooves or cups. the printing ink is forced into the depressions and scraped or wiped off the surrounding higher areas. printing is done with considerable pressure, usually on dampened paper, which sinks into the depressions and ex- tracts ink from them. the depth of the grooves or cups is pro- portionate to the intensity of tone. the deposit of ink extracted from them varies therefore in thickness and, as it is transpar- ent, yields a range of tone proportionate to its density. unlike the other two groups, intaglio plates depend not upon the vari- ation in size of the pointing elements but upon their different intensities. action of light —there are some to different photomechanical processes included in the three general groups, and many more photo-engraving subdivisions of each, but all have for their basis the phenomenon of the action of light, through a negative or diapositive, on a bichromated cmulsion. gelatine, glue, shellac, bitumen and other similar materials, in solution with ammonium bichromate or potassium bichromate, when spread on a supporting base and dried, are rendered insoluble in a ratio directly proportionate to the intensity of light to which they may be exposed. relief and intaglio plates, which are etched, employ this principle to obtain an insoluble photographic image which will act as an acid-resist. all areas not so protected will be subject to attack by the etching acid. in planography, the insoluble areas retain ink and reject moisture, while the soluble hold moisture and reject ink. these principles are fixed, but their application varies in the different processes. photo-engraving—photo-engraving comprises two classes of plates, line and half-tone, although there are many combinations and modifications of these two. a line plate is made from an original comprising definite lines, grains or dots of sulficient size to permit their being photographed, printed on metal and the areas between them etched. if the original comprises tones, as in a photograph or painting, then a half-tone must be em- ployed to reproduce it. it is photographed through a ruled glass cross line screen, placed slightly forward of the photographic plate in the camera. the light from the original, forming the image, spreads in passing across this intervening space, produc- ing dots which vary in size proportionately to its tones. the metal, usually zinc or copper, is coated with a bichromated emulsion and the line or half-tone negative placed in contact with it and exposed to light. that which passes through the transparent areas of the negative renders the emulsion insoluble. the print is washed, removing all soluble emulsion, and heated, producing an insoluble acid-resist of all lines or dots as photo- graphed. the areas between these are etched, leaving the print- ing elements in relief. early relief processes included the swelled gelatine and the washed-out gelatine methods. in the former the gelatine was bichromated and printed from a negative. the soluble areas were then saturated with moisture and allowed to swell sufficiently to make an intaglio of the image, which was then moulded and electrotyped. the washed-out method required that the emulsion be printed in a similar manner, but the gelatine was thicker and the soluble areas were washed away to give the necessary relief for printing. photo-lithography.—this art in its various branches com- prises the entire photomechanical planographic group. only when the lithographic stone is used as a base, is it lithography. when on metal it is called planography, and when on gelatine it is called collotype. the latter embraces such methods as albertype, artotype, heliotype, gelatine printing, aquatone and sperati. the sperati process has the ink repellent incor- porated in the base and requires no dampening roller. the general procedure in all planographic methods is to use a bichromated albumen or gelatine emulsion, printed from either a line, half-tone or continuous tone negative, only the insoluble areas retaining the greasy ink. the sensitised emulsion may be spread on the stone or metal before being printed, or may be printed on one base and transferred to another by means of transfer paper. in the albertype, artotype and other similar methods, the colloids of gelatine are employed to produce the tone variations, each colloid acting as an individual grain or dot. a development in the printing methods of planography is to print from the metal plate to a cylinder covered with a sheet of rubber called an offset blanket. this in turn: prints on the paper the pliable blanket conforming under pressure to the inequalities of the paper. aquatone employs certain features of three different methods. the base is a patented substance, bichro- mated, and printed from a line or hali-tone negative. the printing is by ofiset. the intaglio group—this group includes photogravure, rotagravure, with its many trade names such as rotogravure, alcogravure, art gravure and others, as well as photo-intaglio line engraving and photo-intaglio half-tone engraving. in each of the gravure methods a continuous tone (screenless) diapositive photo-engr aving plate hed areas betwee typ 3 blade scraring ink off surface lara as ald” va vme bel lee yeg lu rection of 77/7 yi prolktion: fic. 1. relief line impression. from pen-and-ink drawing. fic. 2. relief halftone plate impression. from photograph. fic. 1a. photo-micrograph of minute portion of fig. 1. fic. 2a. photo-micrograph of minute portion of fig. 2. fic. 1b. magnification of cross section, line plate (foot of fig. 1a). fic. 2b. magnification of cross section, near foot, of fig. 2a. fic. 3. photo-micrograph of impression from lithographic stone. fic. 4. photo-micrograph of impression from photogravure plate. fic. 3a. magnification of cross section of lithographic stone. fic. 4a. magnification of cross section of photogravure plate. fic. 5. photo-micrograph of impression from rotogravure cylinder. fic. 6. photo-micrograph of impression from intaglio halftone plate. fic. 5a. magnification of cross section of rotogravure cylinder. fic. 6a. magnification of cross section of intaglio halftone plate. impressions from and magnifications of various relief, planographic and intaglio printing processes. all photo-micrographs and drawings of cross sections are magnified about forty-five times. photography is used instead of a negative for photographic printing. as the tonal ranges result from a variation in the depth of each dot or line rather than from their size, it is not necessary to use a half- tone negative. it is essential, however, to establish a cellular structure of grains or dots which may be etched in varying depth. rotogruvure.—in this a special screen of transparent lines is first printed on a bichromated gelatine base mounted on a paper backing. the diapositive is then surprinted and the print de- veloped by washing. the finished print is transferred to a copper cylinder and the paper backing stripped off. the image is represented by gelatine in varying thickness representing its tone range. while insoluble, the gelatine is porous, and in the etching the acid solution seeps through to attack the metal. the seepage is proportionate to the thickness of the gelatine, and a variation in etched depth results. the printing ink is quite fluid and is cleanly scraped off the surface by a thin, razor-edged blade, called a ‘‘ doctor.” photogravure.—in this the plate is flat, and a fine bitumen or resin dust is dropped on it until the metal is about half ob- scured, which is to say that the area of grains is about equal to the areas of exposed metal. the plate is heated, melting the grains and forming a resist called a “ ground.’”’ the print is made on sensitised gelatine, developed and transferred to the prepared metal. the etching principle is similar to that em- ployed in rotogravure, but the spaces between the grains resolve into irregularly shapea cups which vary in depth. a somewhat stiff ink is forced into the depressions and wiped off the surface. photo-intaglio—photo-intaglio line engravings are etched after producing on the metal a resist made by printing from a line diapositive. photo-intaglio half-tone engravings are similar in principle, but are printed from a half-tone diapositive. these methods differ from the rotogravure and photogravure in that the lines or dots, while etched into the metal, print with a varia- tion in size but not in intensity. in different localities these vari- ous processes and methods are known by different names, hence it is impossible to classify them under a universal title, but they have all been described here under photo-engraving, and the subdivisions separately indexed under the descriptive titles gen- erally employed. (see also printing.) ch. a. gx.)",
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