THE SENSATIONS OF TONE Bibliographical Note. First English Edition, June, 1875 ; Second Edition, revised and Aj^pendix added, August, 1885; Third Edition, reprinted from Second Edition, June, 1895. ON THE SENSATIONS OF TONE AS A PHYSIOLOGICAL BASIS FOR THE THEOEY OF MUSIC BY HERMANN L. F. HELMHOLTZ, M.D. LATE FOREIGN MEMBEE OF THE ROYAL SOCIETIES OF LONDON AND EDINBURGH, PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF HEIDELBERG, AND PROFESSOR OF PHYSICS IN THE UNIVERSITY OF BERLIN Trmisluted, thoroughly Revised ami Corrected, rendered conformable to the Fourth (a7id last) German Edition of 1877, with numerous additional Notes and a New additional Appendix bringing doicn information to 1885 and especially adapted to the use of 3Iusical Students BY ALEXANDER J. ELLIS B.A., F.R.S., F.S.A., F.C.P.S., F.C.P. T^\^CE PRESIDENT OF THE PHILOLOGICAL SOCIETY, MEMBER OF THE MATHEMATICAL SOCIETY, FORMERLY SCHOLAR OF TRINITY COLLEGE, CAMBRIDGE, AUTHOR OF ' EARLY ENGLISH PRONUNCIATION ' AND ' ALGEBRA IDENTIFIED WITH GEOMETRY ' THIRD £DITPON LONDON LONGMANS, GREEN, AND CO. AND NEW YORK 1895 All rights reserved PHYSICS DEPT. (JIL.^^Ua^<$>^ ' ABEEDEEN UNIVERSITY PRESS. TRANSLATOR'S NOTICE TO THE SECOND ENGLISH EDITION. Ix preparing a new edition of this translation of Professor Helmlioltz's great work on the Sensations of Tone, which was originally made from the third German edition of 1870, and was finished in June 1875, my first care was to make it exactly conform to i\\e fon,rth German edition of 1877 (the last which has appeared). The numerous alterations made in the fourth edition are specified in the Author's pre- face. In order that no merely verbal changes might escape me, every sentence of my translation was carefully re-read with the German. This has enabled me to correct several misprints and mistranslations which had escaped my previous very careful revision, and I have taken the opportunity of improving the language in many places. Scarcely a page has escaped such changes. Professor Helmholtz's book having taken its place as a work which all candidates for musical degrees are expected to study, my next care was by supplementary notes or brief insertions, always carefully distinguished from the Author's by being inclosed in [ ], to explain any difficulties which the student might feel, and to shew him how to acquire an insight into the Author's theories, which were quite strange to musicians when they appeared in the first German edition of 1863, but in the twenty-two years which have since elapsed have been received as essentially valid by those competent to pass judgment. For this purpose I have contrived the Harmonical, explained on pp. 466-469, by winch, as shewn in numerous footnotes, almost every point of theory can be illustrated ; and I have arranged for its being readily procurable at a moderate charge. It need scarcely be said that my interest in this instrument is purely scientific. My own Appendix has been entirely re-written, much has been rejected and the rest condensed, but, as may be seen in the Contents, I have added a considerable amount of information about points hitherto little known, such as the Determi- nation and History of Musical Pitch, Non-Harmonic scales, Tuning, &c., and in especial I have given an account of the work recently done on Beats and Com- binational Tones, and on Vowel Analysis and Synthesis, mostly since the fourth German edition appeared. Finally, I wish gratefully to acknowledge the assistance, sometimes very great, which I have received from Messrs. D. J. Blaikley,"R. H. M. Bosanquet, Colin Brown, A. Cavaille-Coll, A. J. Hipkins, W. Huggins, F.R.S., Shuji Isawa, H. Ward Poole, R. S. Rockstro, Hermann Smith, Steinway, Augustus Stroh, and James Paid White, as will be seen by referring to their names in the Index. ALEXANDER J. ELLIS. 25 Argyll Road, Kensington July, 1885. 238213 AUTHOR'S PREFACE TO THE FIRST GERMAN EDITION. In laying before the Public the result of eight years' labour, I must first pay a debt of gratitude. The following investigations could not have been accomplished without the construction of new instruments, which did not enter into the inventory of a Physiological Institute, and which far exceeded in cost the usual resources of a German philosopher. The means for obtaining them have come to me from unusual sources. The apparatus for the artificial construction of vowels, described on pp. 121 to 126, I owe to the munificence of his Majesty King Maximilian of Bavaria, to Avhom German science is indebted, on so many of its fields, for ever- ready sympathy and assistance. For the construction of my Harmonium in perfectly natural intonation, descriljcd on p. 316, I was able to use the Soemmering prize which had been awarded me by the Senckenberg Physical Society {die Senckenbergische nahirforscheiide Gesellschaft) at Frankfurt-on-the-Main. While publicly repeating the expression of my gratitude for this assistance in my investi- gations, I hope that the investigations themselves as set forth in this book will prove far better than mere words how earnestly I have endeavoured to make a worthy use of the means thus placed at my conmiand. H. HELMHOLTZ. Heidelberg : October, 1862. AUTHOR'S PREFACE TO THE THIRD GERMAN EDITION. The present Third Edition has been much more altered in some parts than the second. Thus in the sixth chapter I have been able to make use of the new physiological and anatomical researches on the ear. This has led to a modification of my view of the action of Corti's ai'ches. Again, it appears that the pecviliar articulation between the auditory ossicles called 'hammer' and 'anvil' might easily cause within the ear itself the formation of harmonic upper partial tones for simple tones which are sounded loudly. By this means that pecidiar series of upper partial tones, on the existence of which the present theory of music is essentially founded, receives a new subjective value, entirely independent of external alterations in the quality of tone. To illustrate the anatomical descriptions, I have been able to add a series of new woodcuts, principally from Henle's Manual of Anatomy, with the author's permission, for which I here take the opportunity of publicly thankine: him. PREFACE. vii 1 have made many changes iu re-editing the section on the History of Music, and hope that I have improved its connection. I must, however, request the reader to regard this section as a mere compilation from secondaiy sources ; I have neither time nor preliminary knowledge sufficient for original studies in this extremely difficult field. The older history of music to the commencement of Discant, is scarcely more than a confused heap of [secondary subjects, while we can only make hypotheses concerning the principal matters in question. Of course, however, every theoi-y of music must endeavour to bi-ing some order into this chaos, and it cannot be denied that it contains many important facts. For the representation of pitch in just or natural intonation, I have abandoned the method originally proposed by Hauptmann, which was not sufficiently clear in involved cases, and have adopted the system of Herr A. von Oettingen [p. 276] , as had already been done in M. G. Gueroult's French translation of this book. [A comparison of the Third with the Second editions, shewing the changes and additions individually, is here omitted.] If 1 may be allowed in conclusion to add a few words on the reception expe- rienced by the Theory of Music here propounded, I should say that published objections almost exclusively relate to my Theory of Consonance, as if this were the pith of the matter. Those who prefer mechanical explanations express their regret at my having left any room in this field for the action of artistic invention and esthetic inclination, and they have endeavoured to complete my system by new numerical speculations. jT)*'^®^' critics with more metaphysical proclivities have rejected my Theory of Consonance, and with it, as they imagine, my whole Theory of Music, as too coarsely mechanical. ; T hope my critics will excuse me if I conclude from the opposite nature of their objections, that I have struck out nearly the right path. As to my Theory of Consonance, I must claim it to be a mere systematisation of observed facts (with the exception of the functions of the cochlea of the ear, which is moreover an hypothesis that may be entirely dispensed with). But I consider it a mistake to make the Theory of Consonance the essential foundation of the Theory of Music, and I had thought that this opinion was clearly enough expressed in my book. The essential basis of Music is Melody. Harmony has become to \Vestem Euro- peans during the last three centuries an essential, and, to our present taste, indispensable means of strengthening melodic relations, but finely developed music existed for thousands of years and still exists in ultra-European nations, without any hannony at all. And to my metaphysico-esthetical opponents I must reply, that I cannot think I have undervalued the artistic emotions of the human mind in the Theory of Melodic Constmction, by endeavouring to establish the physiological facts on which esthetic feeling is based. But to those who think I have not gone far enough in my physical explanations, 1 answer, that in the first place a natural philosopher is never bound to construct systems about everything he knows and does not know ; and secondly, that I should consider a theory which claimed to have shewn that all the laws of modern Thorough Bass were natural necessities, to stand condemned as having proved too much. Musicians have found most fault with the manner in which I have characterised the Minor Mode. I must refer in reply to those very accessible documents, the musical compositions of a.d. 1500 to a.d. 1750, dm-ing v/hich the modern Minor was developed. These will shew how slow and fluctuating was its development, and that the last traces of its incomplete state are still visible in the works of Sebastian Bach and Handel. Heidelberg : May, 1870. AUTHOR'S PREFACE FOURTH GERMAN EDITION. In the essential conceptions of musical relations I have found nothing to alter in this new edition. In this respect I can but maintain what I have stated in the chapters containing them and in my preface to the third [German] edition. In details, however, much has been remodelled, and in some parts enlarged. As a guide for readers of former editions, I take the liberty to enumerate the following places containing additions and alterations.* P. 16d, note*. — On the French system of counting vibrations. P. 18«. — Appunn and Preyer, limits of the highest audible tones. Pp. 596 to 65b. — On the circumstances under which we distinguish compound sensations. P. 16a, b, c. — Comparison of the upper partial tones of the strings on a new and an old grand pianoforte. P. 83, note f. — Herr Clement Neumann's observations ou the vibrational form of nolin strings. Pp. 89ft to 93&.— The action of blowing organ-pipes. P. 1106.— Distinction of Ou from U. Pp. 1116 to 116a. — The various modifications in the sounds of vowels. P. 145a. — The ampulla? and semicircular canals no longer considered as parts of the organ of hearing. P. 1476. — Waldeyer's and Preyer's measurements adopted. Pp. 1506 to 151d. — On the parts of the ear which perceive noise. P. 1596. — Koenig's observations on combinational tones with tuning-forks. P. 176d, note. — Preyer's observations on deepest tones. P. 179c.— Preyer's observation on the sameness of the quality of tones at the highest pitches. Pp. 203t; to 204«. — Beats between upper partials of the same compound tone condition the preference of musical tones with hannonic upper partials. Pp. 328c to 3296. — Division of the Octave into 53 degi-ees. Bosanquet's harmonivmi. Pp. 338c to 3396. — j\Iodulations tluough chords composed of two major Thirds. P. 365, note t. — Oettingen and Riemann's theory of the minor mode. P. 372. — Improved electro-magnetic driver of the siren. P. 373ft. — Theoretical formulte for the pitch of resonators. P. 374c. — Use of a soap-bubble for seeing vibrations. Pp. 389*:^ to 3966. — Later use of striking reeds. Theory of the blowing of pipes. Pp. 403c to 4056. — Theoretical treatment of svmpathetic resonance for noises. P. 417f^. — A. Mayer's experiments on the audibility of vibrations. P. 428c. d. — Against the defenders of tempered intonation. P. 429. — Plan of Bosanquet's Harmonium. H. HELMHOLTZ. Berlin : A2Jril, 1877. * [The pages of this edition are substituted first edition of this translation are mostly for the German throughout these prefaces, pointed out in footnotes as they arise. — Trans- and omissions or alterations as respects the lator.] CONTENTS. and notes in [ ] are due to the Translator, and the Author is in no way responsible for their contents. Translatoe's Notice to the Second English Edition, p. v. Author's Preface to the First German Edition, p. vi. Author's Preface to the Third German Edition, pp. vi-vii. Author's Preface to the Fourth German Edition, p. viii. Contents, p. ix. List of Figures, p. xv. List of Passages in Musical Notes, p. xvi. List of Tables, p. xvii. INTRODUCTION, pp. 1-6. Relation of Musical Science to Acoustics, 1 Distinction between Physical and Physiological Acoustics, 3 Plan of the Investigation, 4 PAET I. (pp. 7-151.) ON THE COMPOSITION OF VIBRATIONS. Upl^er Partial Tones, and Qualities of Tone. CHAPTEK I. On the Sensation of Sound in General, pp. 8-25. Distinction between Noise and Musical Tone, 8 Musical Tone due to Periodic, Noise to non-Periodic Llotions in the air, 8 General Property of Undulatory Motion : while Waves continually advance, the Particles of the Medium through which they pass execute Periodic ]\Iotions, 9 Differences in Musical Tones due to Force, Pitch, and Quality, 10 Force of Tone depends on Amplitude of Oscillation, Pitch on the length of the Period of Oscillation, 10-14 Simple relations of Vibrational Numbers for the Consonant Intervals, 14 Vibrational Numbers of Consonant Intervals calculated for the whole Scale, 17 Quality of Tone must depend on Vibrational Form, 19 Conception of and Graphical Representation of Vibrational Form, 20 Harmonic Upper Partial Tones, 22 Terms explained : Tone, Musical Tone, Simple Tone, Partial Tone, Compound Tone, Pitch of Compound Tone, 23 CHAPTEE 11. On the Composition of Vibrations, pp. 25-36. Composition of Vv'aves illustrated by waves of water, 25 The Heights of superimposed Waves of Water are to be added algebraically, 27 Corresponding Superimposition of Waves of Sound in the air, 28 CONTENTS. A Composite Mass of Musical Tones will give rise to a Periodic Vibration wlien their Pitch Numbers are Multiples of the same Number, 30 Every such Composite Mass of Tones may be considered to be composed of Simple Tones, 33 This Composition corresponds, according to G. S. Ohm, to the Composition of a Musical Tone from Simple Partial Tones, 33 CHAPTER III. Analysis of Musical Tones by Sympathetic Ee- SONANCE, pp. 36-49. Explanations of the Mechanics of Sympathetic Vibration, 3G Sympathetic Resonance occurs when the exciting vibrations contain a Simple Vibration corresponding to one of the Proper Vibrations of the Sympathising Body, 33 Difference in the Sympathetic Resonance of Tuning-forks and Membranes, 40 Description of Resonators for the more accurate Analysis of Musical Tones, 43 Sympathetic Vibration of Strings, 45 Objective Existence of Partial Tones, 48 CHAPTEE IV. On the Analysis of Musical Tones by the Ear, pp. 49-65. Slethods for observing Upper Partial Tones, 49 Proof of G. S. Ohm's Law by means of the tones of Plucked Strings, of the Simple Tones of Tuning-forks, and of Resonators, 51 Difference between Compound and Simple Tones, 56 Seebeck's Objections against Ohm's Law, 58 The Difficulties experienced in perceiving Upper Partial Tones analytically depend upon a peculiarity common to all human sensations, 59 We practise observation on sensation only to the extent necessary for clearly apprehend- ing the external world, 62 Analysis of Compound Sensations, 63 CHAPTEE Y. On the Differences in the Quality of Musical Tones, pp. 65-119. Noises heard at the beginning or end of Tones, such as Consonants in Speech, or during Tones, such as Wind-rushes on Pipes, not included in the Musical Quality of Tone, which refers to the uniformly continuous musical sound, 65 Limitation of the conception of Musical Quality of Tone, 68 Investigation of the Upper Partial Tones which are present in different Musical Qualities of Tone, 69 1. ]\iusical Tones without Upper Partials, 69 2. Musical Tones with Inharmonic Upper Partials, 70 3. Musical Tones of Strings, 74 Strings excited by Striking, 74 Theoretical Intensity of the Partial Tones of Strings, 79 4. ]\Iusical Tones of Bowed Instruments, 80 5. :Musical Tones of Flute or Flue Pipes, 88 6. ilusical Tones of Reed Pipes, 95 7. Vowel Qualities of Tone, 103 Results for the Character of Musical Tones in general, 118 CHAPTEE YI. On the Apprehension of Qualities of Tone, pp. 119-151. Does Quality of Tone depend on Difference of Phase ? 119 Electro-magnetic Apparatus for answering this question, 121 Artificial Vowels produced by Tuning-forks, 123 How to produce Difference of Phase, 125 Musical Quality of Tone independent of Difference of Phase, 126 Artificial Vowels produced by Organ Pipes, 128 The Hypothesis that a Series of S}-mpathetical Vibrators exist in the ear, explains its peculiar apprehension of Qualities of Tone, 129 Description of the parts of the internal ear which are capable of vibrating sympa- thetically, 129 Damping of Vibrations in the Ear, 142 Supposed Function of the Cochlea, 145 CONTENTS. PAKT 11. (pp. 152-283.) ON THE INTERRUPTIONS OF HARMONY. Gonihinatiomil Tones and Beats, Consonance and Dissonance. CHAPTEE VII. Combinational Tones, pp. 152-159. Combinational Tones arise when Vibrations which are not of infinitesimal magnitude are combined, 152 Description of Combinational Tones, 153 Law determining their Pitch Numbers, 254 Combinational Tones of different orders, 155 Difference of the strength of Combinational Tones on different instruments, 157 Occasional Generation of Combinational Tones in the ear itself, 158 CHAPTEE VIII. On the Beats of Simple Tones, pp. 159-173. Interference of Two Simple Tones of the same pitch, 160 Description of the Polyphonic Siren, for experiments on Interference, 161 Eeinforcement or Enfeeblement of Sound, due to difference of Phase, 163 Interference gives rise to Beats when the Pitch of the two Tones is slightly different, 164 Law for the Number of Beats, 165 Visible Beats on Bodies vibrating sympathetically, 166 Limits of Kapidity of Audible Beats, 1G7 CHAPTEE IX. Deep and Deepest Tones, pp. 174-179. Former Investigations were insufficient, because there was a possibility of the ear being deceived by Upper Partial Tones, as is shewn by the number of Beats on the Siren, 174 Tones of less than thirty Vibrations in a second fall into a Drone, of which it is nearly or quite impossible to determine the Pitch, 175 Beats of the Higher Upper Partials of one and the same Deep Compound Tone, 178 CHAPTEE X. Beats of the Uppee Partial Tones, pp. 179-197. Any two Partial Tones of any two Compound Tones may beat if they are sufficiently near in pitch, but if they are of the same pitch there will be consonance, 179 Series of the different Consonances, in order of 'the Distinctness of their Delimitation, 183 Number of Beats which arise from Mistuning Consonances, and their effect in producing Roughness, 184 Disturbance of any Consonance by the adjacent Consonances, 186 Order of Consonances in respect to Harmoniousness, 188 CHAPTEE XL Beats due to Combinational Tones, pp. 197-211. The Differential Tones of the first order generated by two Partial Tones are capable of producing very distinct beats, 197 Differential Tones of higher orders produce weaker beats, even in the case of simple gene- rating tones, 199 Influence of Quality of Tone on the Harshness of Dissonances and the Harmoniousness of Consonances, 205 CHAPTEE XII. Chords, pp. 211-233. Consonant Triads, 211 Major and Minor Triads distinguished by their Combinational Tones, 214 Relative Harmoniousness of Chords in different Inversions and Positions, 218 Retrospect on Preceding Investigations, 226 CONTENTS. PAKT III. (pp. 234-371.) THE RELATIONSHIP OF MUSICAL TONES. Scales and Tonality. CHAPTEE XIII. General View of the Different Principles OF Musical Style in the Development of Music, pp. 234-249. Difference between the Physical and the Esthetical Method, 234 Scales, Keys, and Harmonic Tissues depend upon esthetic Principles of Style as well as Physical Causes, 235 Illustration from the Styles of Architecture, 235 Three periods of Music have to be distinguished, 236 1. Homophonic Music, 237 2. Polyphonic ]\Iusic, 244 3. Harmonic Music, 246 CHAPTEE XIV. The Tonality of Homophonic Music, pp. 250-290. Esthetical Reason for Progression by Intervals, 250 Tonal Relationship in IMelody depends on the identity of two partial tones, 253 The Octave. Fifth, and Fourth were thus first discovered, 253 Variations in Thirds and Sixths, 255 Scales of Five Tones, used by Chinese and Gaels, 258 The Chromatic and Enharmonic Scales of the Greeks, 262 The Pythagorean Scales of Seven tones, 266 The Greek and Ecclesiastical Tonal ]\Iodes, 267 Early Ecclesiastical Modes, 272 The Rational Construction of the Diatonic Scales by the principle of Tonal Relationship in the first and second degrees gives the five Ancient ^Melodic Scales, 272 Introduction of a more Accurate Notation for Pitch, 276 Peculiar discovery of natural Thirds in the Arabic and Persian Tonal Systems, 280 The meaning of the Leading Note and consequent alterations in the Modern Scales, 285 CHAPTEE XV. The Consonant Chords of the Tonal Modes, pp. 290-309. Chords as the Representatives of compound Musical Tones with peculiar qualities, 290 Reduction of aU Tones to the closest relationship in the popular harmonies of the Manor Mode, 292 ^ i- i- . j Ambiguity of Iifinor Chords, 294 The Tonic Chord as the centre of the Sequence of Chords, 296 Relationship of Chords of the Scale, 297 The ]\Iajor and INIinor IModes are best suited for Harmonisation of all the Ancient Modes, 298 Modern Remnants of the old Tonal IModes, 306 CHAPTEE XVI. The System of Keys, pp. 310-330. Relative and Absolute Character of the different Keys, 310 Modulation leads to Tempering the Intonation of the Intervals, 312 Hauptmann's System admits of a Simplification vfhich makes its Realisation more Practi- cable, 315 Description of an Harmonium with Just Intonation, 316 Disadvantages of Tempered Intonation, 322 Modulation for Just Intonation, 327 CONTENTS. CHAPTEE XVII. Of Discords, pp. 330-350. Envuneration of the Dissonant Intervals in the Scale, 331 Dissonant Triads, 338 Chords of the Seventh, 341 Conception of the Dissonant Note in a Discord, 346 Discords as representatives of compound tones, 347 CHAPTEE XVIII. Laws of Progression of Parts, pp. 350-362. Tlie IMusical Connection of the Notes in a INIelody, 350 Consequent Rules for the Progression of Dissonant Notes, 353 Resolution of Discords, 354 Choral Sequences and Resolution of Chords of the Seventh, 355 Prohibition of Consecutive Fifths and Octaves, 369 Hidden Fifths and Octaves, 3G1 False Relations, 361 CHAPTEE XIX. EsTHETicAL Eelations, pp. 362-371. Review of Results obtained, 362 Law of Unconscious Order in Works of Art, 366 The Law of IMelodic Succession depends on Sensation, not on Consciousness, 368 And similarly for Consonance and Dissonance, 869 Conclusion, 371 APPENDICES, pp. 327-556. I. On an Electro-Magnetic Driving IMachine for the Siren, 372 II. On the Size and Construction of Resonators, 372 III. On the Motion of Plucked Strings, 374 IV. On the Production of Simple Tones by Resonance, 377 V. On tlie Vibrational Forms of Pianoforte Strings, 380 VI. Analysis of the ]\Iotion of Violin Strings, 384 VII. On the Theory of Pipes, 388 A. Influence of Resonance on Reed Pipes, 388 B. Theory of the Blowing of Pipes, 390 I. The Blowing of Reed Pipes, 390 II. The Blowing of Flue Pipes, 394 [Additions by Translator, 396] VIII. Practical Directions for Performing the Experiments on the Composition of Vowels, 398 IX. On the Phases of Waves caused by Resonance, 400 X. Relation between the Strength of Sympathetic Resonance and the Length of Time required for the Tone to die away, 405 XL Vibrations of the Wembrana Basilaris in the Cochlea, 406 XII. Theory of Combinational Tones, 411 XIII. Description of the Mechanism employed for opening the several Series of Holes in the Polyphonic Siren, 413 XIV. Variation in the Pitch of Simple Tones that Beat, 414 XV. Calculation of the Intensity of the Beats of Different Intervals, 415 XVI. On Beats of Combinational Tones, and on Combinational Tones in the Siren and Harmonium, 418 XVII. Plan for Justly-Toned Instruments with a Single Manual, 421 XVIII. Just Intonation in Singing, 422 XIX. Plan of Mr. Bosanquet's Manual, 429 [XX. Additions by the Translator, 430-556 *»* See separate Tables of Contents prefixed to each Section. [Sect. A. On Temperament, 430 [Sect. B. On the Determination of Pitch Numbers, 441 CONTENTS. [App. XX. Additions by the Tra.nsla,toi-—coniinued. *^* See separate Tables of Contents prefixed to each Section. [Sect. C. On the Calculation of Cents from Interval Ratios, 446 [Sect. D. Musical Intervals, not exceeding an Octave, arranged in order of Width 451 ' [Sect. E. On Musical Duodenes, or the Development of Just Intonation for Harmony, 457 [Sect. P. Experimental Instruments for exhibiting the effects of Just Intonation 466 ' [Sect. G. On Tuning and Intonation, 483 [Sect. H. The History of Musical Pitch in Europe, 493 [Sect. K. Non-Harmonic Scales, 514 [Sect. L. Recent Work on Beats and Combinational Tones, 527 [Sect. M. Analysis and Synthesis of Vowel Sounds, 538 [Sect. N. Miscellaneous Notes, 544 [INDEX, 557-576] LIST OF FIGURES 1. Seebeck's Siren, lie 2, 3, 4. Cagniard de la Tour's Siren, 12b 5. Tuning-fork tracing its Curve, 206 6. Curve traced in Phonautograph, 20d 7. Curve of Simple Vibration, 216 8. Curve of ]\Iotion of Hammer moved by Water-wheel, 2lc 9. Curve of :Motion of Ball struck up on its descent, 21c 10. Reproduction of fig. 7, 2M 11. Curve shewing the Composition of a simple Note and its Octave in two different phases, 306, c 12. Curve shewing the Composition of a simple note and its Twelfth in two different phases, 326 13. Tuning-fork on Resonance Box, 40a 14. Forms of Vibration of a Circular Mem- brane, 40f, d 15. Pendulum excited by a membrane covering a bottle, 42« 16. a. Spherical Resonator, 436 b. Cylindi-ical Resonator, 43f 17. Forms of Vibration of Strings, 46«, 6 18. Forms of Vibration of a String de- flected by a Point, 54«, 6 19. Action of such a String on a Sounding- board, 54c 20. Bottle and Blow-tube for producing a simple Tone, 60c 21. Sand figures on circular elastic plates, 71c 22. The Vibration Microscope, 816 23. Vibrations as seen in the Vibration Microscope, 826 •4. Vibrational Forms for the middle of a Viohn String, 836 25. Crumples on the vibrational form of a violin string, 846 26. Gradual development of Octave on a violin string bowed near the bridge, 856 27. An open wooden and stopped metal organ flue-pipe, 88 28. Free reed or Harmonium vibrator, 956 29. Free and striking reed on an organ pipe partly in section, 96rt, 6 30. IMembranous double reed, 97a 31. Reproduction of fig. 12, 120^, b 32. Fork with electro-magnetic exciter, and sliding resonance box with a lid (aa-tificial vowels), 1216 35 33. Fork with electro-magnet to serve as interrupter of the current (artificial vowels), 1226 34. Appearance of figiires seen through the vibration microscope by two forks when the phase changes but the tuning is correct, I26d The same when the tuning is slightly altered, 127ft 56. Construction of the ear, general view, with meatus auditorius, labyrinth, cochlea, and Eustachian tube, 129c 57. The three auditory ossicles, hammer, anvil, and stirrup, in their relative positions, 130c 38. Two views of tlie hammer of the ear, 1316 39. Left temporal bone of a newly-born child with the auditory ossicles in situ, 131c 40. Right drumskin with hammer seen from the inside, 131c 41. Two views of the right anvil, 133« 42. Three views of the right stirrup, 134a 43. A, left labyrinth from without. B, right labyrinth from within. C, left labyrinth from above, 1366, c 44. Utriculus and membranous semicircular canals (left side) seen from without, 137« 45. Bony cochlea (right side) opened in front, 1.37c, d Transverse section of a spire of a cochlea which has been softened in hydrochloric acid, ISSa, b Max Schultze's hairs on the internal surface of the epithsnum in the am^ndkc, 138c, d 48. Expansion of the cochlean nerve, 139c 49. Corti's membrane, 140rt, 6, c 50. Corti's rods or arches separate, 140(/ 51. Corti's rods or arches in situ, 1416, c 52. Diagram of the law of decrease of sym- pathetic resonance, 144c, d Interference of similarly disposed waves, 1606 Interference of dissimilarly disposed waves, 160c 55. Lines of silence of a tuning-fork, 161c 56. The Polyphonic Siren, 162 57. Diagram of origin of beats, 165ff 46. 47. 53. 54. XVI LIST OF PASSAGES IN MUSICAL NOTES. 58. Phouautographic representation of beats, 166rt 59. Identical with fig. 52 but now taken to shew the intensity of beats excited by tones making different intervals, 172c 60. A and B. Diagram of the comparative roughness of intervals in the first and second octaves, 193b, c 61. Diagram of the roughness of dissonant intervals, 333« 62. Reproduction of fig. 24 A, p. 385& 63. Diagram of the motion of a violin string, 387c 14. Diagram of the arrangements for the experiments on the composition of vowels, 399b, c <5. Mechanism for opening the several series of holes in the Polyphonic Siren, 414rt, 16. Section, Elevation, and Plan of Mr. Bosanquet's Manual, 429 Th Additions by Translator. 57. Perspective view of Mr. Colin Brown's Fingerboard, 47 Id 18. Perspective view, 69 plan, 70 section of Mr. H. W. Poole's Keyboard, 475 LIST OF PASSAGES IN MUSICAL NOTES. The small octave, 15fZ The once and twice accented octave, 16a, b The great octave, 166 The first 16 Upper Partials of C'66, 22c The first 8 Upper Partials of 6132, 50«- Prof. Helmholtz's Vowel Resonances, UOb First differential tones of the usual har- monic interval, 1546 Differential tones of different orders of the usual harmonic intervals, 1556, c Summational tones of the usual harmonic intervals, 156ft Examples of beating partials, 180c Coincident partials of the principal con- sonant intervals, 183(Z Coincident converted into beating partials by altering pitch of upper tone, 186c Examples of intervals in which a pair of partials beat 33 times in a second, 1 92« Major Triads with their Combinational Tones, 215a Minor Triads with their Combinational Tones, 2156 Consonant Intervals and their Combina- tional Tones, 218c The most Perfect Positions of the Major Triads, 219c The less Perfect Positions of the Major Triads, 220c The most Perfect Positions of the Minor Triads, 2216 The less Perfect Positions of the INIinor Triads, 221c The most Perfect Positions of Major Tetrads within the Compass of Two Octaves, 223c Best Positions of Minor Tetrads with their false Combinational Tones, 224« Ich bin spatziercn gegangen, 2386 Sic canta comma, 2396 Palestrina's Stabat Mater, first 4 bars, 247c Chinese air after Barrow, 260« Cockle Shells, older form, 2606 Blythe, blythc, and merry are vx, 261ffl Chinese temple hymn after Bitschurin, 2616 Braes of Bulqtihidder, 261c Five Forms of Closing Chords, 291c Two complete closes, 293c IMode of the Fourth, three forms of com- plete cadence, 302(7 Concluding bars of S. Bach's Chorale, Was viein Gott ivill, das gescheJi' allzeit, 3046 End of S. Bach's Hymn, Veni redemptor gentium, 305a Doric cadence from And with His stripes we are healed, in Handel's Messiah, 307a Doric cadence from Hear, Jacob's God, in Handel's Samson, 3076 Examples of False Minor Triad, 340a Examples of Hidden Fifths, 361c? Example of Duodenals, 465c Mr. H. W. Poole's method of fingering and treatment of the harmonic Seventh, 477a Mr, H. W. Poole's Double Diatonic or Di- chordal Scale in Ci' with accidentals, 478a LIST OF TABLES. Pitch Numbers of Notes in Just JMajor Scale, 17« [Scale of Haimonical, '17c, d] [Analogies of notes of the piano and colours of the Spectrum, IBd'] Pitch of the different forms of vibration of a circular membrane, 41c Relative Pitch Numbers of the prime and proper tones of a red free at both ends, 56« Proper Tones of circular elastic plates, 72a Proper Tones of Bells, 72c Proper Tones of Stretched Membranes, 7Sb Theoretical Intensity of the Partial Tones of Strings, 7i'c [Velocity in Soimd in tubes of different diameters — Blaikley, 9Qd] [Partials of £\) Clarinet— Blaikley, 99c] [Harmonics of £\^ horn, 99d] [Compass of Eegisters of male and female voices — Behnke, ] 01 d] Vowel trigram — Du Bois Raymond, senior, 106& Vowel Resonances according to Helmholtz and Donders, l(i9b [Vowel Resonances according to (1) Reyher, [i) Hellwag, (3) Florcke, (4) Donders after Helmholtz, (5) Dondeis after Merkel, (6) Helmholtz, (7) Merkel, (8) Koenig.. (9) Trautmann, 109rf] Willis's Vowel Resonances, 117c [Relative force of the partials for producing different vowels, j24f/] Relation of Strength of Resonance to Alterations of Phase, 12oa Difference of pitch, &c., necessary to reduce sympathetic vibration to J^ of that pro- duced by perfect unisonance, 143a Numbers from wh ich fig. 52 was constructed, 145a Measurements of the basilar membrane in a new-born child, 145c Alteration of size of Corti's rods as they approach the vertex of the cochlea, 145ci [Preyer's distinguishable and undistin- guishable intervals, 147f/] First differential tones of the usual har- monic intervals, L'.4« [Differential tones of different orders of the usual harmonic intervals, 155(/] Different intervals which would give 33 beats of their primes, 172a [Pitch numbers of Appunn's bass reeds, 1776] [Experiments on audibility of very deep tones, 177c] Coincident partials for the principal con- sonances, 183a Pitch numbers of the primes which make consonant iaitei-vals with a tone of 300 vib., 184c Beating partials of the notes in the last table with a note of 301 vib., and number of beats, 184c^ Disturbance of a consonance by altering one of its tones by a Semitone, 185c Influence of different consonances on each other, 187b [Upper partials of a just Fifth, 188d] [Upper partials of an altered Fifth, 189c] [Comparison of the upper partials of a Fourth and Eleventh, major Sixth and major Thirteenth, minor Sixth and minor Thirteenth, lS9c?and 1906, c] [Comparison of the upper partials of a major and a minor Third, 190c?] [Comparison of the uj^per partials of aU the usual consonances, pointing out those which beat, 1916, c] [Comparison of the upper partials of septimal consonances, involving the seventh partial, and pointing out which beat, 195c, d] [General Table of the first 16 harmonics of C'66, shewing how they affect each other in any combination, 197c, d] Table of partials of 200 and 301, shewing their differential tones, 198c Table of possible triads, shewing consonant, dissonant, and septimal intervals, 2126, c Table of consonant triads, 214a [The first 16 harmonics of C, 2Ud] [Calculation of the Combinational Tones of the Major Triads, 214rf] [Most of the first 40 harmonics oiA^,\f, 215c] [Calculation of the Combinational Tones of the Minor Triads, 21:>d] [Calculation of the Differential Tones of the Major Triads in their most Perfect Positions, 2l9d] [Calculation of the Combinational Tones of the Major Triads in the less Perfect Positions, 220d] [Calculation of the Combinational Tones of LIST OF TABLES. the Minor Triads in the most and less Perfect Positions of the Minor Triads, 221d, d'] [Calculation of the false Combinational Tones of Minor Tetrads in their best positions, 224f?] Ecclesiastical Modes, 245c, d Partial Tones of the Tonic, 257a [Pentatonic Scales, 259c, d] [Tetrachords 1 to 8, with intervals in cents, 263d'] Greek Diatonic Scales, 267c [Greek Diatonic Scales with the intervals in cents, 268c] [Greek Diatonic Scales reduced to begin- ning with c, with the intervals in cents, 268f^'] Greek modes with the Greek Ecclesiastical and Helmholtzian names, 269a Later Greek Scale, 270a Tonal Keys, 270c Ecclesiastical Scales of Ambrose of Milan, 2716, c The Five Melodic Tonal Modes, 272b [The Seven Ascending and Descending Scales, compared with Greek, with inter- vals in cents, 274e, d] [The different scales formed by a dif- ferent choice of the intercalary tones, 277c', rf'] The Five Modes with variable intercalary tones, 278a, b [J. Curwen's characters of the tones in the major scale, 279&, c] [Arabic Scale in relation to the major Thirds, 281rf'] Arabic Scales, 2826-283c [Prof. Land's account of the 12 Arabic Scales, 284 note] Five Modes as formed from three chords each, 293c?, 294a The same with double intercalary tones, 297c, d The same, final form, 2986, c Trichordal Eelations of the Tonal Modes, :309rf [Thirds and Sixths in Just, Equal, and Pythagorean Intonation compared, 313c] [Combinational Tones of Just, Equal, and Pythagorean Intonation compared, 314(i] The Chordal System of Prof. Helmholtz's Just Harmonium, 316c [Duodenary statement of the tones on Prof. Helmholtz's Just Harmonium, 317c, d] The Chordal System of the minor keys on Prof. Helmholtz's Just Harmonium, 318a, b, d [Table of the relation of the Cycle of 58 to Just Intonation, 3296, c] [Tabular Expression of the Diagram, fig. 61, 332] [Table of Roughness, 3ZM] Measurements of Glass Resonators, 373c Measurements of resonance tubes men- tioned on p. 55a, Z77d Table of tones of a conical pipe of zinc, calculated from formula 393c [with sub- sidiary tables, 393c? and 394c] Table of Mayer's observations on numbers of beats, 418a Table of four stops for a single manual justly intoned instrument, 421c Table of five stops for the same, 422a In the Additions by Translator. Table of Pythagorean Intonation, 4336, c Table of Meantone Intonation, 4346 Table of Equal Intonation, 437c, d Synonymity of Equal Temperament, 4386 Synonymity of Mr. Bosanquet's Notes in Fifths, 439a Notes of Mr. Bosanquet's Cycle of 53 in order of Pitch, 4396, c, d Expression of Just Intonation in the Cycle of 1200, p. 440 Principal Table for calculation of cents, 450a, Auxiliary Tables, 451a Table of Intervals not exceeding one Octave, 4536 Unevenly numbered Harmonics up to the D3rd, 457a Number of any Interval not exceeding a Tritone, contained in an Octave, 457c Harmonic Duodene or Unit of Modulation, 461a The Duodenarium, 463a Fingerboard of the Harmonical, first four Octaves, with scheme, 4676, fifth Octave, 468rf Just Harmonium scheme, 470a Just English Concertina scheme, 4706 Mr. Colin Brown's Voice Harmonium Fingerboard and scheme, 471a Rev. Henry Liston's Organ and scheme, 4736 Gen. Perronet Thompson's Organ scheme, A7Zd Mr. H. Ward Poole's 100 tones, 474c Mr. H. W. Poole's scheme for keys of F, C, G, 476a Mv. Bosanquet's Generalised Keyboard, 480 Expression of the degrees of the 53 divi- sion by multiples of 2, 5 and 7, p. 481c Typographical Plan of Mr. J. Paul White's Fingerboard, 4826 Specimens of tuning in Meantone Tem- perament, 484c Specimens of tuning in Equal Tempera- ment, 4856 Pianoforte Tuning — Fourths and Fifths, 485d Cornu and Mercadier's observation on Violin Intonation, 486c to 4876 LIST OF TABLES. Scheme for tuning in Equal Temperament, 4895 Proof of rule for tuning in Equal Tempera- ment, 490e, d Proof of rule for Tuning in Meantoue Tem- perament, 492« Historical Pitches in order from Lowest to Highest, 49 5« to 504rt Classified Index to the last Table, ri04& to Effects of the length of the foot in differ- ent countries on the pitch of organs, 512a Non-harmonic scales, 514c to 519c Vowel sound ' Oh ! ' Analysis at various pitches by Messrs. Jenkin & Ewing, 539d to 5416 Vowel sounds ' oo,' 'awe,' 'ah,' analysis at various pitches by Messrs. Jenkin & Ewing, p. 541c, d Mean and actual Compass of the Human Voice, 545«, b, e True Tritonic, False Tritonic, Zarlino's, Meantone and Equal Temperaments, compared, 548a Presumed Characters of Major and Minor Keys, 551-«, h INTEODUCTION. In the present work an attempt will be made to connect the boundaries of two sciences, which, although drawn towards each other by many natural atiinities, have hitherto remained practically distinct — I mean the boundaries of physical and physiological acoustics on the one side, and of musical science and esthetics on the other. The class of readers addressed will, consequently, have had very different cultivation, and will be affected by very different interests. It will therefore not be superfluous for the author at the outset distinctly to state his intention in undertaking the work, and the aim he has sought to attain. The horizons of physics, philosophy, and art have of late been too widely separated, and, as a consequence, the language, the methods, and the aims of any one of these studies present a certain amount of difficulty for the student of any other H of them ; and possibly this is the principal cause why the problem here undertaken has not been long ago more thoroughly considered and advanced towards its solution. It is true that acoustics constantly employs conceptions and names borrowed from the theory of harmony, and speaks of the 'scale,' 'intervals,' ' consonances,' and so forth ; and similarly, manuals of Thorough Bass generally begin with a physical chapter which speaks of ' the numbers of vibrations,' and fixes their 'ratios' for the different intervals; but, up to the present time, this apparent connection of acoustics and music has been wholly external, and may be regarded rather as an expression given to the feelmg that such a connection must exist, than as its actual formulation. Physical knowledge may indeed have been useful for musical instrument makers, but for the development and foundation of the theory of harmony H It has hitherto been totally barren. And yet the essential facts within the field here to be explained and turned to account, have been known from the earliest times. Even Pythagoras (fl. circa B.C. 540-510) knew that when strings of different lengths but of the same make, and subjected to the same tension, were used to give the perfect consonances of the Octave, Fifth, or Fourth, their lengths must be in the ratios of 1 to 2, 2 to '6, or 3 to 4 respectively, and if, as is probable, his knowledge was partly derived from the Egyptian priests, it is impossible to conjecture in what remote antiquity this law was first known. Later physics has extended the law of Pythagoras by passing from the lengths of strings to the number of vibra- tions, and thus making it applicable to the tones of all musical instruments, and the numerical relations 4 to 5 and 5 to «i have been added to the above u - PLAN OF THE WORK. introd. for the less perfect consonances of the major and minor Thirds, but I am not aware that any real step was ever inade towards answering the ques- tion : What have musical consonances to do ivith the ratios of the first six numbers ! Musicians, as well as philosophers and physicists, have generally contented themselves with saying in effect that human minds were in some unknown manner so constituted as to discover the numerical relations of musical vibrations, and to have a peculiar pleasure in contemplating simple ratios which are readily comprehensible. Meanwhile musical esthetics has made unmistakable advances in those points which depend for their solution rather on psychological feeling than on the action of the senses, by introducing the conception of movement in IT the examination of musical works of art. E. Hanslick, in his book On the Beautiful in Music {Ueher das musihalisch Schone), triumphantly attacked the false standpoint of exaggerated sentimentality, from which it was fashionable to theorise on music, and referred the critic to the simple elements of melodic movement. The esthetic relations for the structure of musical compositions, and the characteristic differences of individual forms of composition are explained more fully in Vischer's Esthetics (Aesthetik). In the inorganic world the kind of motion we see, reveals the kind of moving force in action, and in the last resort the only method of recognising and measuring the elementary powers of nature consists in determining the motions they generate, and this is also the case for the motions of bodies or of voices which take place under the influence of human feelings. Hence ^the properties of musical movements which possess a graceful, dallying, or a heavy, forced, a dull, or a powerful, a quiet, or excited character, and so on, evidently chiefly depend on psychological action. In the same way questions relating to the equilibrium of the separate parts of a musical composition, to their development from one another and their connection as one clearly intelligible whole, bear a close analogy to similar questions in architecture. But all such investigations, however fertile they may have been, cannot have been otherwise than imperfect and uncertain, so long as they were without their proper origin and foundation, that is, so long as there was no scientific foundation for their elementary rules relating to the construction of scales, chords, keys and modes, in short, to all that is usually contained in works on ' Thorough Bass '. In this elementary region U we have to deal not merely with unfettered artistic inventions, but with the natural power of immediate sensation. Music stands in a much closer connection with pure sensation than any of the other arts. The latter rather deal with what the senses apprehend, that is with the images of outward objects, collected by psychical processes from immediate sensation. Poetry aims most distinctly of all at merely exciting the formation of images, by addressing itself especially to iinagination and memory, and it is only by subordinate auxiliaries of a more musical kind, such as rhythm, and imitations of sounds, that it appeals to the immediate sensation of hearing. Hence its efltects depend mainly on psychical action. The plastic arts, although they make use of the sensation of sight, address the eye almost in the same way as poetry addresses the ear. Their main purpose is to excite in us the image of an external object of determinate form and colour. The spectator is essentially intended to interest himself in this iN-TROD. PLAN OF THE WORK. 3 image, and enjoy its beauty ; not to dwell upon the means by which it was created. It must at least be allowed that the pleasure of a connoisseur or virtuoso in the constructive art shown in a statue or a picture, is not an essential element of artistic enjoyment. It is only in painting that we find colour as an element which is directly appreciated by sensation, without any intervening act of the intellect. On the contrary, in music, the sensations of tone are the material of the art. So far as these sensations are excited in music, we do not create out of them any images of external objects or actions. Again, when in hearing a concert we recognise one tone as due to a violin and another to a clarinet, our artistic enjoyment does not depend upon our conception of a violin or clarinet, but solely on our hearing of the tones they produce, whereas the ^ artistic enjoyment resulting from viewing a marble statue does not depend on the white light which it reflects into the eye, but upon the mental image of the beautiful human form which it calls up. In this sense it is clear that music has a more immediate connection with pure sensation than any other of the fine arts, and, consequentl}^, that the theory of the sensations of hearing is destined to play a much more important part in musical esthetics, than, for example, the theory of chiaroscuro or of perspective in painting. Those theories are certainly useful to the artist, as means for attaining the most perfect representation of nature, but they have no part in the artistic effect of his work. In music, on the other hand, no such perfect representation of nature is aimed at ; tones and the sensations of tone exist for themselves alone, and produce their effects independently "^ of anything behind them. This theory of the sensations of hearing belongs to natural science, and comes in the first place under ^A?/sio/o^/<;«/ rtco/^s^/c.s\^ Hitherto it is the physical part of the theory of sound that has been almost exclusively treated at length, that is, the investigations refer exclusively to the motions produced by solid, liquid, or gaseous bodies when they occasion the sounds which the ear appreciates. This physical acoustics is essentially nothing but a section of the theory of the motions of elastic bodies. It is physically indifferent whether observations are made on stretched strings, by means of spirals of brass wire (which vibrate so slowly that the eye can easily follow their motions, and, consequently, do not excite any sensation of sound), or by means of a violin string (where the eye can scarcely perceive the vibrations ^i which the ear readily appreciates). The laws of vibratory motion are pre- cisely the same in both cases ; its rapidity or slowness does not affect the laws themselves in the slightest degree, although it compels the observer to apply different methods of observation, the eye for one and the ear for the other. In physical acoustics, therefore, the phenomena of hearing are taken into consideration solely because the ear is the most convenient and handy means of observing the more rapid elastic vibrations, and the physicist is compelled to study the peculiarities of the natural instrument which he is employing, in order to control the correctness of its indications. In this way, although physical acoustics as hitherto pursued, has, undoubtedly, collected many observations and much knowledge concerning the action of the ear, which, therefore, belong to physiolocjical aconstics, these results were not the principal object of its investigations ; they were merely secondary B 2 4 PLAN OF THE WORK. introd. and isolated facts. The only justification for devoting a separate chapter to acoustics in the theory of the motions of elastic bodies, to which it essentially belongs, is, that the application of the ear as an instrument of research influenced the nature of the experiments and the methods of observation. But in addition to a physical there is a physiological theory of acousticSy the aim of v^hich is to investigate the processes that take place within the ear itself. The section of this science which treats of the conduction of the motions to which sound is due, from the entrance of the external ear to the expansions of the nerves in the labyrinth of the inner ear, has received much attention, especially in Germany, since ground was broken by 11 Johannes Mueller. At the same time it must be confessed that not many results have as yet been established with certainty. But these attempts attacked only a portion of the problem, and left the rest untouched. Investigations into the processes of each of our organs of sense, have in general three different parts. First we have to discover how the agent reaches the nerves to be excited, as light for the eye and sound for the ear. This may be called the physical part of the corresponding physiological investigation. Secondly we have to investigate the various modes in which the nerves themselves are excited, giving rise to their various sensations, and finally the laws according to which these sensations result in mental images of determinate external objects, that is, in perceptions. Hence we have secondly a specially physiological investigation for sensations, and 11 thirdly, a specially psychological investigation for perceptions. Now whilst the physical side of the theory of hearing has been already frequently attacked, the results obtained for its physiological and psychological sections are few, imperfect, and accidental. Yet it is precisely the physio- logical part in especial — the theory of the sensations of hearing — to which the theory of music has to look for the foundation of its structure. In the present work, then, I have endeavoured in the first place to collect and arrange such materials for the theory of the sensations of hearing as already existed, or as I was able to add from my own personal investigations. Of course such a first attempt must necessarily be somewhat imperfect, and be limited to the elements and the most interesting divisions of the subject discussed. It is in this light that I wish these studies to be regarded. 11 Although in the propositions thus collected there is little of entn-ely new discoveries, and although even such apparently new facts and observations as they contain are, for the most part, more properly speaking the imme- diate consequences of my having more completely carried out known theories and methods of investigation to their legitimate consequences, and of my having more thoroughly exhausted their results than had hare- tofore been attempted, yet I cannot but think that the facts frequently receive new importance and new illumination, by being regarded from a fresh point of view and in a fresh connection. The First Part of the following investigation is essentially physical and physiological. It contains a general investigation of the phenomenon of harmonic uppier partial tones. The nature of this phenomenon is established, and its relation to qnality of tone is proved. A series of qualities of tone are analysed in respect to their harmonic upper partial tones, and it results iNTROD. PLAN OF THE WORK. 5 that these upper partial tones are not, as was hitherto thought, isolated phenomena of small importance, but that, with very few exceptions, they determine the qualities of tone of almost all instruments, and are of the greatest importance for those qualities of tone which are best adapted for musical purposes. The question of how the ear is able to perceive these harmonic upper partial tones then leads to an hypothesis respecting the mode in which the auditory nerves are excited, which is well fitted to reduce all the facts and laws in this department to a relatively simple mechanical conception. The Second Part treats of the disturbances produced by the simultaneous production of two tones, namely the comhimitional tones and heat:. The physiologico-physical investigation shows that two tones can besimul-^ taneously heard by the ear without mutual disturbance, when and only when they stand to each other in the perfectly determinate and well-known relations of intervals which form musical consonance. We are thus imme- diately introduced into the field of music proper, and are led to discover the physiological reason for that enigmatical numerical relation announced by Pythagoras. The magnitude of the consonant intervals is independent of the quality of tone, but the harmoniousness of the consonances, and the distinctness of their separation from dissonances, depend on the quality of tone. The conclusions of physiological theory here agree precisely with the musical rules for the formation of chords ; they even go more into par- ticulars than it was possible for the latter to do, and have, as I believe, the authority of the best composers in their favour. ^ In these first two Parts of the book, no attention is paid to esthetic considerations. Natural phenomena obeying a blind necessity, are alone treated. The Third Part treats of the construction of musical scales and )wtes. Here we come at once upon esthetic ground, and the differences of national and individual tastes begin to appear. Modern music has especially developed the principle of tonality, which connects all the tones in a piece of music by their relationship to one chief tone, called the tonic. On admitting this principle, the results of the preceding investigations furnish a method of constructing our modern musical scales and modes, from which all arbitrary assumption is excluded. I was unwilling to separate the physiological investigation from its musical consequences, because the correctness of these consequences must H be to the physiologist a verification of the correctness of the physical and physiological views advanced, and the reader, who takes up my book for its musical conclusions alone, cannot form a perfectly clear view of the meaning and bearing of these consequences, unless he has endeavoured to get at least some conception of their foundations in natural science. But in order to facihtate the use of the book by readers w^ho have no special knowledge of physics and mathematics, I have transferred to appendices, at the end of the book, all special instructions for performing the more comphcated experiments, and also all mathematical investigations. These appendices are therefore especially intended for the physicist, and contain the proofs of my assertions.* In this way I hope to have consulted the interests of both classes of readers. * [The additional Appendix XX. bj' the Translator is intended especially for the use of musical students. — Translator.] 6 PLAN OF THE WORK. ixtrod. It is of course impossible for any one to understand the investigations thoroughly, who does not take the trouble of becoming acquainted by per- sonal observation with at least the fundamental phenomena mentioned. Fortunately with the assistance of common musical instruments it is easy for any one to become acquainted with harmonic upper partial tones, com- binational tones, beats, and the like.* Personal observation is better than the exactest description, especially when, as here, the subject of investiga- tion is an analysis of sensations themselves, which are always extremely difficult to describe to those who have not experienced them. In my somewhat unusual attempt to pass from natural philosophy into the theory of the arts, I hope that I have kept the regions of physiology H and esthetics sufficiently distinct. But I can scarcely disguise from myself, that although my researches are confined to the' lowest grade of musical grammar, they may probably appear too mechanical and unworthy of the dignity of art, to those theoreticians who are accustomed to summon the enthusiastic feelings called forth by the highest works of art to the scientific investigation of its basis. To these I would simply remark in conclusion, that the following investigation really deals only with the analysis of actually existing sensations — that the physical methods of observation employed are almost solely meant to facilitate and assure the work of this analysis and check its completeness — and that this analysis of the sensations would suffice to furnish all the results required for musical theory, even independently of my physiological hypothesis concerning the mechanism of ^ hearing, already mentioned (p. oa), but that I was unwilling to omit that hypothesis because it is so well suited to furnish an extremely simple con- nection between all the very various and very complicated phenomena which present themselves in the course of this investigation. t * [But the use of the H(trmonical, described London, ]Macmillan, 1873. Such readers will in App. XX. sect. F. No. 1, and invented for also find a clear exposition of the physical the purpose of illustrating the theories of this relations of sound in J. Tyndall, On Souiul, work, is recommended as greatly superior for a course of eight lectures, London, 1867, (the students and teachers to any other instrument. last or fourth edition 188.3) Longmans, Green, — Transhitor.'] & Co. A German translation of this work, t Readers unaccustomed to mathematical entitled Der Schall, edited by H. Helmholtz and physical considerations will find an and G. Wiedemann, was published at Bruns- abridged account of the essential contents of wick in 1874. this Ijook in Sedley Taylor, Sound and Musk, *^* [The marks ^ in the outer margin of each page, separate the page into 4 sections, referred to as a, >>, c, d, placed after the number of the page. If any section is in doul)le columns, the letter of the second column is accented, as p. i:3.r.] PART I. ON THE COMPOSri'ION OF YIBHATIONS, uppp:r partial tones, a^td qualttib:s of toxe. CHAPTER I. ox THE SENSATION OF SOUND IN GENERAL. Sensations result from the action of an external stimulus on the sensitive apparatus of oiir nerves. Sensations differ in kind, partly with the organ of sense excited, and partly with the nature of the stimulus employed. Each organ of sense pro- duces peculiar sensations, which cannot be excited by means of any other; the eye gives sensations of light, the ear sensations of sound, the skin sensations of touch. Even when the same sunbeams which excite in the eye sensations of light, impinge on the skin and excite its nerves, they are felt only as heat, not as light, wt In the same way the vibration of elastic bodies heard by the ear, can also be felt by the skin, but in that case produce only a whirring fluttering sensation, not sound. The sensation of sound is therefore a species of reaction against external stimulus, peculiar to the ear, and excitable in no other organ of the body, and is completely distinct from the sensation of any other sense. As our problem is to study the laws of the sensation of hearing, our fir:jt business will be to examine how many kinds of sensation the ear can generate, and what differences in the external means of excitement or sound, correspond to these differences of sensation. The first and principal difference between various sounds experienced by our ear, is that between 7ioises and musical tom^s. The soughing, howling, and whistling of the wind, the splashing of water, the rolling and rumbling of carriages, are examples of the first kind, and the tones of all musical instruments of the second. Noises and musical tones may certainly intermingle in very various degrees, and *t pass insensibly into one another, but their extremes are widely separated. The nature of the difference between musical tones and noises, can generally be determined by attentive aural observation without artificial assistance. We perceive that generally, a noise is accompanied by a rapid alternation of different kinds of sensations of sound. Think, for example, of the rattling of a carriage over granite paving stones, the splashing or seething of a waterfall or of the waves of the sea, the rustling of leaves in a wood. In all these cases we have rapid, irregular, but distinctly perceptible alternations of vr.rious kinds of sounds, which crop up fitfully. When the wind howls the alternation is slow, the sound slowly and gradually rises and then falls again. It is also more or less possible to separate restlessly alternating sounds in case of the greater number of other noises. We shall hereafter become acquainted with an instrument, called a resonator, which will materially assist the ear in making this separation. On the other hand, a musical tone strikes the ear as a perfectly luidisturbed, luiiform sound which 8 NOISE AND MUSICAL TONE. tart i. remains unaltered as long as it exists, and it presents no alternation of various kinds of constituents. To this then corresponds a simple, regular kind of sensation, whereas in a noise many various sensations of musical tone are irregularly mixed up and as it were tumbled about in confusion. We can easily compound noises out of musical tones, as, for example, by simultaneously striking all the keys con- tained in one or two octaves of a pianoforte. This shows us that musical tones are the simpler and more regular elements of the sensations of hearing, and that we have consequently first to study the laws and peculiarities of this class of sensations. Then comes the further question : On what difterence in the external means of excitement does the difference between noise and musical tone depend 1 The normal and usual means of excitement for the human ear is atmospheric vibration. ^ Tiie irregularly alternating sensation of the ear in the case of noises leads us to conclude that for these the vibi-ation of the air must also change irregularl}'. For musical tones on the other hand we anticipate a regular motion of the air, con- tiniiing uniformly, and in its turn excited by an equally regular motion of the sonorous body, whose impulses were conducted to the ear by the air. Those regular motions which produce musical tones have been exactly investi- gated by physicists. They are oscillations, vibrations, or swings, that is, up and down, or to and fro motions of sonorous bodies, and it is necessary that these oscillations should be regularly perioilic. By a periodic motion we mean one which constantly returns to the same condition after exactly equal intervals of time. The length of the equal intervals of time between one state of the motion and its next exact repetition, we call the length of the oscillation, vibration, or swing, or the period of the motion. In what manner the moving body actually moves during one period, is perfectly inditterent. As illustrations of periodical motion, take the ^motion of a clock pendulum, of a stone attached to a string and whirled round in a circle with uniform velocity, of a hammer made to rise and fall uniformly by its connection with a water wheel. All these motions, however different be their form, are periodic in the sense here explained. The length of their periods, which in the cases adduced is generally from one to several seconds, is relatively long in comparison with the much shorter periods of the vibrations producing nuisical tones, the lowest or deepest of which makes at least 30 in a second, while in other cases their number may increase to several thousand in a second. Our definition of periodic motion then enables us to answer the question pro- posed as follows : — The sensation of a musical tone is due to a rapid periodic inotion of the sonorous body ; the sensation of a noise to non-periodic motions. The musical vibrations of solid bodies are often visible. Although they may be too rapid for the eye to follow them singly, wc easily recognise that a sounding- string, or tuning-fork, or the tongue of a reed-pipe, is rapidly vibrating between two ^ fixed limits, and the regulai", apparently immovable image that we see, notwith- standing the real motion of the body, leads us to conclude that the backward and forward motions are quite regular. In other cases we can feel the swinging motions of sonorous solids. Thus, the player feels the trembling of the reed in the mouth- piece of a clarinet, oboe, or bassoon, or of his own lips in the mouthpieces of trumpets and trombones. The motions proceeding from the sounding bodies are usually conducted to our ear by means of the atmosphere. The particles of air must also execute periodi- cally recurrent vibrations, in order to excite the sensation of a musical tone in our ear. This is actually the case, although in daily experience sound at first seems to be some agent, which is constantly advancing through the air, and projjagating itself further and further. We must, however, here distinguish between the motion of the individual particles of air — which takes place periodically backwards and forwards within very narrow limits — and the propagation of the sonorous tremor. The latter is constantly advancing by the constant attraction of fresh particles into its sphere of tremor. CHAP. I. PROPAGATION OF SOUND. 9 This is a peculiarity of all so-called ii)i m 1584 316| 633f 24 : 25 5 : 6 70 316 E, 82 .i 165 3.30 660 15 : 16 4 : 5 112 386 F 88 176 352 704 8 :9 3:4 204 498 G 99 198 396 792 15: 16 2 : 3 112 702 A'\y 105j 211i 422| 8444 24 : 25 5: 8 70 814 ^1 110 220 440 880 20 : 21 3:5 85 884 -B'r, 11.5^ 231 462 924 35 : 36 4 :7 49 969 B^b 1184 237f 475i 950| 24 : 25 5:9 70 1018 B\ 123= 247* 495 990 8: 15 — 1088 15 : 16 112 c 132 1 264 528 1056 1 : 2 — 1200 Translator.'] t [The following account of the actual tones 3d is adapted from my History of Musical Fitch. G , commencement of the 32-foot oc- tave, the 'lowest tone of verj' large organs, two C 18 COMPASS OF INSTRUMENTS. with 33 viljivations, and the latest grand pianos even down to A^^ with 27^ vibra- tions. On larger organs, as already mentioned, there is also a deeper Octave reach- ing to C„ with 16i vibrations. But the musical character of all these tones below F^ is imperfect, because we are here near to the limit of the power of the ear to combine vibrations into musical tones. These lower tones cannot therefore be vised musically except in connection with their higher octaves to which they impart a character of o-reater depth without rendering the conception of the pitch indeterminate. Upwards, pianofortes generally reach a"" with b520, or even c" with 4224 vibra- tions. The highest tone in the orchestra is probably the five-times accented J" of the piccolo flute with 4752 vibrations. Appunn and W. Preyer by means of small tunino--forks excited by a violin bow have even reached the eight times accented «="" with 40,960 vibrations in a second. These high tones were very painfully unplea- sant, and the pitch of those which exceed the boundaries of the musical scale was ^ very imperfectly discriminated by musical observers."* More on this in Chap. IX. The musical tones which can be used with advantage, and have clearly dis- tinguishable pitch, have therefore between 40 and 4000 vibrations in a second, extendino- over 7 octaves. Those which are audible at all have from 20 to 40,000 vibrations, extending over about 11 octaves. This shows what a great variety of different pitch numbers can be perceived and distinguished by the ear. In this respect the ear is far superior to the eye, which likewise distinguishes light of dif- ferent periods of vibration by the sensation of different colours, for the compass of the vibrations of light distinguishable by the eye but slightly exceeds an Octave.t Fo7re and 2}itch were the two first differences which we found between musical tones ; the third was quality of tone, which we have now to investigate. When of Tone,' [ilbcr die Grcnzen dcr Tonv:ahrnc]i- muncj, 1876, p. 20), are in the South Kensing- ton Museum, Scientific Collection. I have several times tried them. I did not myself find the tones painful or cutting, probably because there was no beating of inharmonic upper ^Dartials. It is best to sound them with two violin bows, one giving the octave of the other. The tones can be easily heard at a distance of more than 100 feet in the gallery of the Museum. — Translator.'] t [Assuming the undulatory theory, which attributes the sensation of light to the vibra- tions of a supposed luminous ' ether,' resem- bling air but more delicate and mobile, then the phenomena of ' interference ' enables us to calculate the lengths of waves of light in empty space, &c. , hence the numbers of vibra- tions"in a second, and consequently the ratios of these numbers, which will then clearly resemble the ratios of the pitch nimibers that measure musical intervals. Assuming, then, that the yellow of the spectriun answers to the tenor c in music, and Fraunhofer's ' line A ' corresponds to the G below it, Prof. Helm- holtz, in his Physiological Optics, {Hand- buch der physiologischen Optik, 1867, p. 237), gives the following analogies between the notes of the piano and the colours of the spectrmn :— Octaves below the lowest tone of the Violon- cello. A,„ the lowest tone of the largest pianos. C\, commencement of the 16-foot octave, the lowest note assigned to the Double U Bass in Beethoven's Pastoral Symphony. JS,, the lowest tone of the German four-stringed Double Bass, the lowest tone mentioned in the text. F„ the lowest tone of the English four-stringed Double Bass. G,, the lowest tone of the Italian three- stringed Double Bass. A„ the lowest tone of the English three-stringed Double Bass. C, conmiencement of the 8-foot octave, the lowest tone of the Violoncello, written on the second leger line below the bass stafi. G, the tone of the third open string of the Violoncello. c, commencement of the 4-foot octave ' tenor C,' the lowest tone of the Viola, written on the second space of the bass staff, d, the tone of the second open string of the Violoncello. /, the tone signified by the bass or i^-clef. ;/, the lowest tone of the Violin, a, the tone of the highest open string of the Violoncello, c', conmiencement of the 51 2-foot octave, ' middle 6',' written on the leger line between the bass and treble staves, the tone signified by the tenor or C-clef . d', the tone of the third open string of the Violin, g', the tone signified by the treble or G-clei. a', the tone of the second open string of the Violin, the 'tuning note ' for orchestras, t", commencement of the 1-foot octave, the usual ' tuning note ' for pianos. e", the tone of the first or highest open string of the Violin, c", commencement of the ^-foot octave, g'", the usual highest tone of the Flute. Civ, commencement of the ^-foot octave. €'", the highest tone on the Violin, being the double Octave harmonic of the tone of the highest open string, a}"", the usual highest tone of large pianos. tZ^', the highest tone of the piccolo flute. c^"i, the highest tone reached by Appunn's forks, see next note. — Translator.} * [Copies of these forks, described in Prof. Preyer's essay ' On the Limits of the Perception F 1 end of the Red. G,Iied. f i, Violet. ■(/, Ultra-violet. G i Red. ^,*Red. ^t' " ((,„ .. A 5, Orange-red. ^,X>range. b, end of the solar spectrum. c. Yellow. The scale there- c it. Green. fZ, Greenish-blue. fore extends to about a Fourth d |, Cyanogen-blue. e, Indigo-blue. beyond the oc- tave. — 2'ransla- /, Violet. tor.] CHAP. I. QUALITY OF TONE AND FORM OF VIBRATION. 19 we hear notes of the same force and same pitch sonnded snccessively on a piano- forte, a vioUn, clarinet, oboe, or trumpet, or by the liuman voice, the character of the musical tone of each of these instruments, notwithstanding the identity of force and pitch, is so different that by means of it we recognise witli the greatest ease which of these instruments was used. Varieties of quality of tone appear to be infinitely numerous. Not only do we know a long series of musical instruments which could each produce a note of the same pitch ; not only do diflerent individual instruments of the same species, and the voices of different individual singers show certain more delicate shades of quality of tone, which our ear is able to distinguish ; but notes of the same pitch can sometimes be sounded on the same instrument with several qualitative varieties. In this respect the ' bowed ' instruments (i.e. those of the violin kind) are distinguished above all other. But the human voice is still richer, and human speech employs these very qualitative varieties of tone, in order to distinguish different letters. The different vowels, namely, belong to the class H of sustained tones which can be used in music, while the character of consonants mainly depends upon brief and transient noises. On inquiring to what external physical difference in the waves of sound the different qualities of tone correspond, we must remember that the amplitude of the vibration determines the force or loudness, and the period of vibration the pitch. Quality of tone can therefore depend upon neither of these. The only possible hypothesis, therefore, is that the quality of tone should depend upon the manner in which the motion is performed within the period of each single vibra- tion. For the generation of a musical tone we have only required that the motion should be periodic, that is, that in any one single period of vibration exactly the same state should occur, in the same order of occurrence as it presents itself in any other single period. As to the kind of motion that should take place within any single period, no hypothesis was made. In this respect then an endless variety of motions might be possibly for the production of sound. ^ Observe instances, taking first such periodic motions as are performed so slowly that -we can follow them with the eye. Take a pendulum, which we can at any time construct by attaching a weight to a thread and setting it in motion. The pendulum swings from right to left with a imiform motion, uninterrupted by jerks. Near to either end of its path it moves slowly, and in the middle fast. Among sonorous bodies, which move in the same way, only very much faster, we may . mention tuning-forks. When a tuning-fork is struck or is excited by a violin bow, and its motion is allowed to die away slowly, its two prongs oscillate backwards and forwards in the same way and after the same law as a pendulum, only they make many hundred swings for each single swing of the pendulum. As another example of a periodic motion, take a hammer moved by a water- wheel. It is slowly raised by the millwork, then released, and falls down suddenly, is then again slowly raised, and so on. Here again we have a periodical backwards and forwards motion ; but it is manifest that this kind of motion is totally diflf'erent ^ from that of the pendulum. Among motions wdiich produce musical sounds, that of a violin string, excited by a bow, would most nearly correspond with the hammer's, as will be seen from the detailed description in Chap. V. The string clings for a time to the bow, and is carried along by it, then suddenly releases itself, like the hammer in the mill, and, like the latter, retreats somewhat with much greater velocity than it advanced, and is again caught by the bow and carried forward. Again, imagine a ball thrown up vertically, and caught on its descent with a blow which sends it up again to the same height, and suppose this operation to be performed at equal intervals of time. Such a ball would occupy the same time in rising as in falling, but at the lowest point its motion would be suddenly interrupted, whereas at the top it wovdd pass through gradually diminishing speed of ascent into a gradually increasing speed of descent. This then would be a third kind of alternating periodic motion, and would take place in a manner essentially different from the other two. c 2 20 FORM OF VIBRATION. To render the law of such motions more comprehensible to the eye than is le by lengthy verbal descriptions, mathematicians and physicists are in the habit of applying a graphical method, which must be frequently employed in this work, and should therefore be well understood. To render this method intelligible suppose a drawing point b, fig. 5, to be fastened to the prong A of a tuning-fork in such a manner as to mark a surface of pauer B B. Let the tuning-fork be moved with a uniform velocity in the direc- tion of the upper arrow, or else the paper be drawn under it in the opposite direction, as shown by the lower arrow. When the fork is not sounding, the point will describe the dotted straight line d c. But if the prongs have been first set in vibration, the point will describe the undulating line d c, for as the prong vibrates, the attached point b will constantly move backwards and forwards, and hence be ^ sometimes on the right and sometimes on the left of the dotted straight line d c, as is shown by the wavy line in the figure. This wavy line once drawn, remains as a permanent image of the kind of motion performed by the end of the fork during ^ its musical vibrations. As the point b is moved in the direction of the straight line d c with a constant velocity, equal sections of the straight line d c will corre- spond to equal sections of the time during which the motion lasts, and the distance of the wavy line on either side of the straight line will show how far the point b has moved from its mean position to one side or the other during those sections of time. In actually performing such an experiment as this, it is best to wrap the paper over a cylinder which is made to rotate uniformly by clockwork. The paper is wetted, and then passed over a turpentine flame which coats it with lampblack, on which a fine and somewhat smooth steel point will easily trace delicate lines. Fig. 6 is the copy of a drawing actually made in this way on the rotating cylinder of Messrs. Scott and Koenig's Phonmttograph. Fig. 7 shows a portion of this curve on a larger scale. It is easy to see the meaning of such a curve. The drawing point has passed with a uniform velocity in the direction e h. Suppose that it has described the section e g in -^^ of a second. Divide e g into 12 equal parts, as in the figure, then the point has been y^o^ of a second in describing the length of any such section horizontally, and the curve shows us on what side and at what distance from the position of rest the vibrating point will be at the end of ■^~-^, yf^, and so on, of a second, or, generally, at any given short interval of time since it left the point e. We see, in the figure, that after yi^ of a second it had reached the height 1, and that it rose gradually till the end of yf ^ of a second ; then, however, it began to descend gradually till, at the end of Tfo = oV seconds, it had reached its mean FORM OF VUUIATION. 21 position f, and then it continued descending on the (j{)posite side till the end of y^ of a second and so on. We can also easily determine where the vibrating point was to be found at the end of any fraction of this hundred-and-twentieth of a second. A drawing of this kind consequently shows immediately at what point of its path a vibrating particle is to be found at any given instant, and hence gives a complete image of its motion. If the reader wishes to reproduce the motion of the vibrating point, he has only to cut a narrow vertical slit in a piece of paper, and place it over fig. 6 or fig. 7, so as to show a vei-y small portion of the curve through the vertical slit, and draw the book slowly but uniformly under the slit, from right to left ; the white or black point in the slit will then appear to move backwards and forwards in precisely the same manner as the original drawing point attached to the fork, only of course much more slowly. We are not yet able to make all vibrating bodies describe their vibrations U directly on paper, although nmch methods required for this purpose. has recently been made in the are able ourselves to draw such progress But we curves for all sounding bodies, when the law of their motion is known, that is, when we know how far the vibrating point will be from its mean position at a,ny given moment of time. We then set off on a horizontal line, such as e f, fig. 7, lengths corresponding to the interval of time, and let fall perpendiculars to it on^ either side, making their lengths equal or proportional to the distance of the vibrat- ing point from its mean position, and then by joining the extremities of these per- pendiculars we obtain a curve such as the vibrating body would have drawn if it had been possible to make it do so. Thus fig. 8 represents the motion of the hammer raised by a water-wheel, or of a point in a string excited by a violin bow. For the first 9 intervals it rises slowly and xuiiformly, and during the 10th it falls suddenly down. LiA. V Fig. 9 represents the motion of the ball which is struck up again as soon as it^ "comes down. Ascent and descent are performed with equal rapidity, whereas in fig. 8 the ascent takes much longer time. But at the lowest point the blow suddenly changes the kind of motion. Physicists, then, having in their mind such curvilinear forms, representing the law of the motion of sounding bodies, speak briefly of the form of vibratum of a sounding body, and assert that the (juality of tone depends on the form of vibration. This assertion, which has hitherto been based simply on the fact of our knowing that the quality of the tone could not possibly depenfl on the periodic time of a vibration, or on its amplitude (p. 10c), will be strictly examined hereafter. It will be shown to be in so far correct that every different quality of tone recpiires a difterent form of vibration, but on the other hand it will also appear that different forms of vibration may correspond to the same quality of tone. On exactly and carefully examining the effect produced on the ear by difterent forms of vibration, as for example that in fig. 8, corresponding nearly to a violin 22 COMPOUND AND PARTIAL TONES. part i. string, we meet with a strange and imexpected phenomenon, long known indeed to individual musicians and ph^'sicists, but commonly regarded as a mere curiosity, its generality and its great significance for all matters relating to musical tones not having been recognised. The ear when its attention has been properly' directed to the effect of the vibrations which strike it, does not hear merely that one musical tone whose pitch is determined by the period of the vibrations in the manner already explained, but in addition to this it becomes aware of a whole series of higher musical tones, which we will call the harmonic upper partial tones, and sometimes simply the iipper jMrtials of the whole musical tone or note, in contra- distinction to the fundamental or prime x>'[? c" d' e" ^y fi" ^^'a" ~h"\) h" c" Ordinal mmher of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Pitch mfmber 66 132 198 264 380 396 462 528 594 660 726 792 858 924 990 1054* where the figures [in the first line] beneath show how many times the corresponding pitch number is greater than that of the prime tone [and, taking the lowest note to have 66 vibrations, those in the second line give the pitch numbers of all the *\ other notes]. The whole sensation excited in the ear by a periodic vibration of the air we * [This diagram has been slightly altered to This slightly flattens each note, and slow beats introduce all the first 16 harmonic partials can be produced in ever_v case (except, of of C 66 (which, excepting 11 and 13, are course, 11 and 13, which are not on the given on the Harmouical as harmonic notes), instrument) up to 16. It should also be ob- aiid to show the notation, symbolising, both in served that the pitch of the beat is very nearly letters and on the staff, the 7th, 11th, and that of the upper {not the lower) note in each 13th harmonic partials, which are not used in case. The whole of these 16 harmonics of C 66 general music. It is easy to show on the (except the 11th and 13th) can Ije played Harmonical that its lowest note, C of this at once on the Harmonical by means of the series, contains all these partials, after the harmonical bar, first without and then with theory of the beats of a disturbed unison the 7th and 14th. The whole series will be has been explained in Chap. VIII. Keep found to sound like a single fine note, and the down the note C, and touch in succession the 7th and 14th to materially increase its rich- notes c, g, c', c', cj', &c., but in touching the latter ness. The relations of the partials in this case press the fmger-key such a little way down may be studied from the tables in the footnotes that the tone of the note is only just audible. to Chap. X. — Translator.'] DEFINITION OF TERMS EMPLOYED. 23 have called a mHsica/ tone. We now find that this is ronijjoujtd, c()ntainin<>- a series of ditt'erent tones, which we distinguish as the constituents or 2M)-tial tones of the compound. The first of these constitnents is the pritne j^artial tone of the compoiuid, and the rest its harmonic upper partial tones. The number which shows the order of any partial tone in the series shows how many times its vibrational number exceeds that of the prime tone.* Thus, the second partial tone makes twice as many, the third three times as many vibrations in the same time as the prime tone, and so on. G. S. Ohm was the first to declare that there is only one form of vibration which will give rise to no harmonic upper partial tones, and which will therefore consist solely of the prime tone. This is the form of vibration which we have described above as pecidiar to the pendulum and tmiing-forks, and drawn in figs. G and 7 (p. 10). We will call these j^^ndular vibrations, or, since they caiuiot be analysed into a compound of diflferent tones, simple vibrations. In what sense not H merely other musical tones, but all other forms of vibration, may be considered as compowid, will be shown hereafter (Chap. IV.). The terms simple or pendular vibration, f will therefore be used as synonymous. We have hitherto used the expression tone and musical tone indifferently. It is absolutely necessary to dis- tinguish in acoustics first, a musical tone, that is, the impression made by an// periodical vibration of the air ; secondW, a simple tone, that is, the impression l)roduced by a simpde or pendular vibration of the air ; and thirdly a comjwund tone, that is, the impression produced by the simultaneous action of several simple tones with certain definite ratios of pitch as already explained. A musical tone may be either simjde or comptound. For the sake of brevity, tone will be used in * [The ordinal number of a partial tone in general, must be distinguished from the ordinal number of an upper partial tone in particular. For the same tone the former number is always greater by unity than the latter, because the partials in general include the prime, which is reckoned as the first, and the upper partials exclude the prime, which being the loudest partial is of course not an upper partial at all. Thus the partials gene- rally numbered 2 3 4 5 6 7 8 9 are the same as the upper partials numbered 12 3 4 5 6 7 8 respectively. As even the Author has occasionally failed to carry out this distinction in the original German text, and other writers have constantly neglected it, too much weight cannot be here laid upon it. The presence or absence of the word wppcr before the word partml must always be care- fully observed. It is safer never to speak of an vipper partial by its ordinal number, but to call the pfth upixr partial the sixth partial, omitting the word uyper and increasing the 51 ordinal number by one place. And so in other cases. — Translator.'] t The law of these vibrations may be popularly explained by means of the constritc- tion in fig. 10. Suppose a point to describe the circle of which c is the centre with a uniform velocity, and that an observer stands at a considerable distance in the prolongation of the line e h, so that he does not see the surface of the circle but only its edge, in which case the point will appear merely to move up and down along its diameter a b. This up and down motion would take place exactl}- according to the law of pendular vibration. To represent this motion graphi- cally by means of a curve, divide the length e g, supposed to correspond to the time of a single period, into as many (here 12) equal parts as the circumference of the circle, and draw the perpendiculars 1, 2, 3, &c., on the dividing points of the line e g, in order, equal in length to and in the same direction with, those drawn in the circle from the correspond- ing points 1, 2, 3, &c. In this way we obtain the curve drawn in fig. 10, which agrees in form witli that drawn by the tuning-fork, fig. 6, p. 206, but is of a larger size. Mathe- matically expressed, the distance of the vibrat- ing point from its mean position at any time is equal to the sine of an arc proportional to the corresponding time, and hence the form of simple vibrations are also called the sivc- vibrations [and the above curve is also known as the curve of sines']. 24 DEFINITION OF TERMS EMPLOYED. the general sense of a musical tone, leaving the context or a prefixed tjualitication to determine whether it is simple or compound. A compound tone will often bo briefly called a note, and a simple tone will also be frequently called a imrtial, when used in connection with a compound tone : otherwise, the full expression simple tone will be employed. A note has, properly speaking, no single pitch, as it is made up of various partials each of which has its own pitch. By the 2'''^^'^^ of a note or compo^ind tone then we shall therefore mean the ^)?YcA of its lowest pjartial or prime tone. By a chord or combination of tones we mean several musical tones (whether simple or compound) produced by difl^erent instruments or diff'erent parts of the same instrument so as to be heard at the same time. • The facts here adduced show us then that every musical tone in which harmonic upper partial tones can be distinguished, although produced by a single instrument, may really be con- sidered as in itself a chord or combination of various simple tones.* H * [The above paragraph relating to the English terms used in this translation, neces- sarily differs in many respects from the original, in which a justification is given of the use made by the Author of certain German ex- pressions. It has been my object to employ terms which should be thoroughly English, and should not in any way recall the German words. The word tone in English is extremely ambiguous. Prof. Tj'ndall {Lectures on Sound, 2nd ed. 1869, p. 117) has ventured to define a tone as a sini/ile lone, in agreement with Prof. Helmholtz, who in the present passage limits the German word Ton in the same way. But I felt that an English reader could not be safely trusted to keep this very peculiar and important class of musical tones, which he has very rarely or never heard separately, invariably distinct from those musical tones •fl with which he is familiar, unless the word tone were uniformly qualified by the epithet simple. The only exception I could make was in the case of a partial tone, which is received at once as a new conception. Even Prof. Helmholtz himself has not succeeded in using his word Ton consistently for a simple tone only, and this was an additional warning to me. English musicians have been also in the habit of using tone to signify a certain musical interval, and semitone for half of that interval, on the equally tempered scale. In this case I write Tone and Semitone with capital initials, a practice which, as already explained (note, p. 13c?'), I have found con- venient for the names of all intervals, as Thirds, Fifths, &c. Prof. Helmholtz uses the word Klang for a musical tone, which gene- ^ rally, but not always, means a compound tone. Prof. Tyndall (ibid.) therefore proposes to use the English word clang in the same sense. But clang has already a meaning in English, thus defined by Webster : ' a sharp shrill sound, made by striking together metallic substances, or sonorous bodies, as the clang of arms, or any like sound, as the claiig of trumpets. This word implies a degree of harshness in the sound, or more harshness than clink.' Interpreted scientifically, then, clang according to this definition, is either noise or one of those musical tones until in- harmonic upper partials, which will be sub- sequently explained. It is therefore totally unadapted to represent a musical tone in general, for which the simple word tone seems eminently suited, being of course originally the tone produced by a stretched string. The coiomon word note, properly the mark by which a musical tone is written, will also, in accordance with the general practice of musi- cians, be used for a musical tone, which is generally compound, without necessarily im- plying that it is one of the few recognised tones in our musical scale. Of course, if clang could not be used. Prof. Tyndall's suggestion to translate Prof. Helmholtz's Klangfarbc by clangtint (ibid.) fell to the ground. I can find no valid reason for sup- planting the time-honoured expression qualitg of tone. Prof. Tyndall [ibid.) quotes Dr. Young to the effect that ' this quality of sound is sometimes called its register, colour, or timbre'. Register has a distinct meaning in vocal music which must not be disturbed. Timbre, properly a kettledrum, then a helmet, then the coat of arms surmounted with a helmet, then the official stamp bearing that coat of arms (now used in France for a postage label), and then the mark which declared a thing to be what it pretends to be, Burns's 'guinea's stamp,' is a foreign word, often odiously mispronounced, and not worth preserving. Colour I have never met with as applied to music, except at most as a passing metaphorical expression. But the difference of tones in qualitg is familiar to our language. Then as to the Partial Tones, Prof. Helmholtz uses Theiltone and Particd- tone, which are aptly Englished by partial simple tones. The words simple and tone, however, may be omitted when partials is employed, as partials are necessarily both tones and simple. The constituent tones of a chord may be either simple or compound. The Grundion or fundamental tone of a compound tone then becomes its prime tone, or briefly its prime. The Grundton or root of a chord will be further explained hereafter. Upper partial (simple) tones, that is, the partials exclusive of the prime, even when harmonic (that is, for the most part, belong- ing to the first six partial tones), must be distinguished from the sounds usually called harmonics when produced on a violin or harp for instance, for such harmonics are not neces- sarily simple tones, but are more generally compounds of some of the complete series of j)artial tones belonging to the musical tone of the whole string, selected by damping the remainder. The fading harmonics heard in listening to the sound of a pianoforte string, struck and undamped, as the sound dies away, are also compound and not simple partial tones, but as they have the successive partials for their successive primes, they have the CHAPS. I. 11. COEXISTENCE OF DISTINCT WAVES OF SOUND. 25 Now, since quality of tone, as we have seen, depends on the form of vibration, which also determines the occurrence of upper partial tones, we have to inquire how far differences in quality of tone depend on different force or loudness of upper partials. This inq\iiry will be found to give a means of clearing- up our concep- tions of what has liitherto been a perfect enigma, — the nature of quality of tone. And we must then, of course, attempt to explain how the ear manages to analyse every musical tone into a series of partial tones, and what is the meaning of this analysis. These investigations will engage our attention in the following chapters. CHAPTER II. ON THE COMPOSITION OF VIBRATIONS. A.T the end of the last chapter we came upon the remarkable fact that the human ear is capable, under certain conditions, of separating the musical tone produced by a single musical instrument, into a series of simple tones, namely, the prime partial tone, and the various upper partial tones, each of which produces its own separate sensation. That the ear is capable of distinguishing from each other tones proceeding from different sources, that is, which do not arise from one and the same sonorous body, we know from daily experience. There is no difficulty during a concert in following the melodic progression of each individual instru- ment or voice, if we direct our attention to it exclusively ; and, after some practice, most persons can succeed in following the simultaneous progression of several united parts. This is true, indeed, not merely for musical tones, but also for noises, and for mixtures of music and noise. When several persons are speaking at once, we can generally listen at pleasure to the words of any single one of them, H and even understand those words, provided that they are not too much overpowered by the mere loudness of the others. Hence it follows, first, that many different trains of waves of sound can be propagated at the same time through the same mass of ail-, without mutual disturbance ; and, secondly, that the human ear is capable of again analysing into its constituent elements that composite motion of the air which is produced by the simultaneous action of several musical instru- ments. We will first investigate the nature of the motion of the air when it is produced by several simultaneous musical tones, and how such a compound motion is distinguished from that due to a single musical tone. We shall see that the ear has no decisive test by which it can in all cases distinguish between the effect of a pitch of those partials. But these fading meaning upper, but the English preposition harmonics are not regular compound tones of over is equivalent to the German preposition the kind described on p. 22«, because the lower iiher. Compare Obcrzolm, &n 'upper tooth,' ^ partials are absent one after another. Both i.e., a tooth in the upper jaw, with UeherzaJm, sets of harmonics serve to indicate the exist- an ' overtooth,' i.e., one grown over another, ence and place of the partials. But they are a projecting tooth. The continual recurrence no more those upper partial tones themselves, of such words as cJancj, clancjtint, overtone, than the original compound tone of the string would combine to give a strange un-English is its own prime. Great confusion of thought appearance to a translation from the German, having, to my own knowledge, arisen from On the contrary I have endeavoured to put it conionndiug such ha rmunics with tqjpcr parti(il into as straightforward EngHsh as possible. tones, I have generally avoided using the am- But for those acquainted with the original and biguous substantive Af/r/iwy/uV. Properly speak- with Prof. Tyndall's work, this explanation ing the harmonics of any compound tone are seemed necessary. Finally I would caution other compound tones of which the primes are the reader against using overtones for partial partials of the original compound tone of tones in general, as almost every one who which they are said to be harmonics. Prof. adopts Prof. Tyndall's word is in the habit of Helmholtz's term Oherfihie is merely a con- doing. Indeed I have in the course of this traction for Oberpartiattonc, but the casual translation observed, that even Prof. Helmholtz resemblance of the sounds of ober and over, has himself has been occasionally misled to em- led Prof. Tyndall to the erroneous translation ploy Obertone in the same loos^e manner. See overtones. The German ober is an adjective my remarks in note, p. 23f. — Translator.] 26 COMPOSITION OF WAVES. part i. motion of the air caused by several different musical tones arising from different sources, and that caused by the musical tone of a single sounding body. Hence the ear has to analyse the composition of single musical tones, under proper con- ditions, by means of the same faculty which enabled it to analyse the composition of simultaneous musical tones. We shall thus obtain a clear concei^tion of v.-hat is meant by analysing a single musical tone into a series of partial simple tones, and we shall perceive that this phenomenon depends upon one of the most essential and fundamental properties of the human ear. We begin by examining the motion of the air which corresponds to several simple tones acting at the same time on the same mass of air. To illustrate this kind of motion it will be again convenient to refer to the waves foi-med on a calm surface of water. We have seen (p. 9a) that if a point of the surface is agitated by a stone thrown upon it, the agitation is propagated in rings of waves over the surface f to more and more distant points. Now, throw two stones at the same time on to different points of the surface, thus producing two centres of agitation. Each will give rise to a separate ring of waves, and the two rings gradually expanding, will finally meet. Where the waves thus come together, the water will be set in motion by both kinds of agitation at the same time, but this in no wise prevents botli series of waves from advancing further over the surface, just as if each were alone present and the other had no existence at all. As they proceed, those parts of both rings which had just coincided, again appear separate and mialtered in form. These little waves, caused by throwing in stones, may be accompanied by other kinds of waves, such as those due to the wind or a passing steamboat., Our circles of waves will spread out over the water tluis agitated, with the same quiet regularity as they did upon the calm surface. Neither will the greater waves be essentially disturbed by the less, nor the less by the greater, provided the waves never break ; if that happened, their regular course would certainly be impeded. H Indeed it is seldom possible to survey a large surface of water from a high point of sight, without perceiving a great multitude of different systems of waves mutually overtopping and crossing each other. This is best seen on the surface of the sea, viewed from a lofty cliff, when there is a lull after a stiff breeze. We first see the great waves, advancing in far-stretching ranks from the blue distance, here and there more clearly marked oiit by their white foaming crests, and following one another at regular intervals towards the shore. From the shore they rebound, in different directions according to its sinuosities, and cut obliquely across the advancing waves. A passing steamboat forms its own wedge-shaped wake of waves, or a bird, dai'ting on a fish, excites a small circular system. The eye of the spectator is easily able to pursue each one of these diHerent trains of waves, great and small, wide and narrow, straight and curved, and observe how each passes over the surface, as undisturbedly as if the water over which it flits Avere not agitated at the same time by other motions and other forces. I must own that II whenever I attentively observe this spectacle it awakens in me a peculiar kind of intellectual pleasure, because it bares to the bodily eye, what the mind's eye grasps only by the help of a long series of complicated conclusions for the waves of the invisible atmospheric ocean. We have to imagine a perfectly similar spectacle proceeding in the interior of a ball-room, for instance. Hera we have a number of musical instruments in action, speaking men and women, rustling garments, gliding feet, clinking glasses, and so on. All these causes give rise to systems of waves, which dart through the mass of air in the room, are reflected from its walls, return, strike the opposite wall, are again reflected, and so on till they die out. We have to imagine that from the mouths of men and from the deeper musical instruments there proceed waves of from 8 to 12 feet in length [c to F], from the lips of the women waves of 2 to 4 feet in length [c" to c'], from the rustling of the dresses a fine small crumple of wave, and so on ; in short, a tumbled entanglement of the most difterent kinds of motion, complicated beyond conception. CHAP. II. ALGEBRAICAL ADDITIOX OF WAVES. 27 And yet, ;is the ear is able to distinguish all the sei)arate constituent parts of this confused whole, we are forced to conclude that all these different systems of wave coexist in the mass of air, and leave one another mntually undisturbed. But how is it possible for them to coexist, since every individual train of waves has at any particular point in the mass of air its own particular degree of condensa- tion and rarefaction, which determines the velocity' of the particles of air to this side or that ? It is evident that at each point in the mass of air, at each instant of time, there can be only one single degree of condensation, and that the particles of air can be moving with only one single determinate kind of motion, having only one single determinate amount of velocity, and passing in only one single deter- minate direction. What happens under such circumstances is seen directly by the eye in the waves of water. If where the water shows large waves we throw a stone in, tiie waves thus caused will, so to speak, cut into the larger moving surface, and thislj surface will be partly raised, and partlj- depressed, by the new waves, in such a way that the fresh crests of the rings will rise just as much above, and the troughs sink just as much below the curved surfaces of the previous larger waves, as they would have risen above or svink below the horizontal surface of calm water. Hence where a crest of the smaller system of rings of waves comes upon a crest of the greater system of waves, the surface of the water is raised by the sum of the two heights, and where a trough of the former coincides with a trough of the latter, the surface is depressed by the sum of the two depths. This may be expressed more briefly if we consider the heights of the crests above the level of the surface at rest, as positive magnitudes, and the depths of the troughs as negative magnitudes, and then form the so-called algebraical sum of these positive and negative magnitudes, in which case, as is well known, two positive magnitudes (heights of crests) must be added, and similarly for two negative magnitudes (depths of troughs) ; but when both negative and positive concur, one is to be subtracted U from the other. Performing the addition then in this algebraical sense, we can express our description of the surface of the water on which two systems of waves concur, in the following simple manner : The distance of the surface of the water at any point from its jjosition of rest is at any moment eqiial to the [alyeljraica/] sum of the distances at vjliich it ^vould have stood had each wave acted separately at the same jjlace and at the same time. The eye most clearly and easily distinguishes the action in such a case as has been just adduced, where a smaller circular system of waves is produced on a large rectilinear system, because the two systems are then strongly distinguished from each other both by the height and shape of the waves. But with a little attention the eye recognises the same fact even when the two systems of waves have but slightly diff"erent forms, as when, for example, long rectilinear waves advancing towards the shore concur with those reflected from it in a slightly different direction. In this case we observe those well-known comb-backed waves where H the crest of one system of waves is heightened at some points by the crests of the other system, and at others depressed by its troughs. The multiplicity of forms is here extremely great, and any attempt to describe them would lead us too far. The attentive observer will readily comprehend the result by examining any disturbed surface of water, without further description. It will s\iffice for our purpose if the first example has given the reader a clear conception of what is meant by adding waves together/'' Hence although the surface of the water at any instant of time can assume only one single form, while each of two different systems of waves simultaneously attempts to impress its own shape upon it, we are able to suppose in the above * Tho velocities and displacements of the addition of waves as is spoken of in the text, particles of water are also to be added accord- is not perfectly correct, unless the heights of ing to the law of the so-called parallelogram the waves are infinitely small in comparison of forces. Strictly speaking, such a simple with their lengths. 28 ALGEBRAICAL ADDITION OF WAVES. part i. sense that the two systems coexist and are superimposed, by considering the actual elevations and depressions of the surface to be suitably separated into two parts, each of which belongs to one of the systems alone. In the same sense, then, there is also a superimposition of different systems of sound in the air. By each train of waves of sound, tlie density of the air and the velocity and position of the particles of air, are temporarily altered. There are places in the wave of sound comparable with the crests of the waves of water, in which the quantity of the air is increased, and the air, not having free space to escape, is condensed ; and other places in the mass of air, comparable to the troughs of the waves of water, having a diminished quantity of air, and hence diminished density. It is true that two different degrees of density, produced by two different systems of waves, cannot coexist in the same place at the same time ; nevertheless the condensations and rarefactions of the air can be (algebraically) H added, exactly as the elevations and depressions of the surface of the water in the former case. Where two condensations are added we obtain increased condensation, where two rarefactions are added we have increased rarefaction ; while a concur- rence of condensation and rarefaction mutually, in whole or in part, destroy or neutralise each other. The displacements of the particles of air are compounded in a similar manner. If the displacements of two different systems of waves are not in the same direc- tion, they are compounded diagonally ; for example, if one system would drive a particle of air upwards, and another to the right, its real path will be obliquely upwards towards the right. For our present purpose there is no occasion to enter more particularly into such compositions of motion in different directions. We are only interested in the effect of the mass of air upon the ear, and for this we are only concerned with the motion of the air in the passages of the ear. Now the passages of our ear are so narrow in comparison with the length of the waves of ^ sound, that we need only consider such motions of the air as are parallel to the axis of the passages, and hence have only to distinguish displacements of the particles of air outwards and inwards, that is towards the outer air and towards the interior of the ear. For the magnitude of these displacements as well as for their velocities with which the particles of air move outwards and inwards, the same (algebraical) addition holds good as for the crests and troughs of waves of water. Hence, vjhen several sonorous bodies in the surroxmding atmosphere, simnl- taneously excite different systems of waves of sound, the changes of density of the air, and the disj)lacements and velocities of the ^)a^*^?'c^6's of the air ivithin the passages of the ear, are each equal to the [algebraical) sum of the corresponding changes of density, disjolacements, and- velocities, inhich each system of waves would have sejmrately produced, if it had acted independently ; * and in this sense we can say that all the separate vibrations which separate waves of sound would H have produced, coexist undisturbed at the same time within the passages of our ear. After having thus in answer to the first question explained in what sense it is possible for several different systems of waves to coexist on the same surface of water or within the same mass of air, we proceed to determine the means possessed by our organs of sense, for analysing this composite whole into its original consti- tuents. I have already observed that an eye which surveys an extensive and disturbed surface of water, easily distinguishes the separate systems of waves from each other and follows their motions. The eye has a great advantage over the ear in being able to survey a large extent of surface at the same moment. Hence the eye readily sees whether the individual waves of water are rectilinear or curved, and whether they have the same centre of curvature, and in what direction they * The same is true for the whole mass of according to the law of the parallelogram of external air, if only the addition of the dis- forces, placements in different dii'ections is made CHAP. II. EYE AND EAR C'ONTRASTED. 29 are advancin"'. All these observations assist it in determining whotlier two systems of waves are connected or not, and hence in discovering their corresponding parts. Moreover, («i the snrface of the water, waves of unequal length advance with unecpial velocities, so that if they coincide at one moment to such a degree as to be difficult to distinguish, at the next instant one train pushes on and the other lags behind, so that they become again separately visible. In this way, then, the observer is greatly assisted in referring each system to its point of departure, and in keeping it distinctly visible during its further course. For the eye, then, two systems of waves having difterent points of departure can never coalesce ; for example, such as arise from two stones thrown into the water at different points. If in any one place the rings of wave coincide so closely as not to be easily separable, they always remain separate during the greater part of their extent. Hence the eye could not be easily brought to confuse a compound with a simple undulatory motion. Yet this is precisely what the ear does under similar circum-H stances when it separates the musical tone which has proceeded from a single source of sound, into a series of simple partial tones. But the ear is much more unfavourably situated in relation to a system of waves of sound, than the eye for a system of waves of water. The ear is affected only by the motion of that mass of air which happens to be in the immediate neigh- bourhood of its tympanum within the aural passage. Since a transverse section of the aural passage is comparatively small in comparison with the length of waves of sound (which for serviceable musical tones varies from 6 inches to .32 feet),* it corresponds to a single point of the mass of air in motion. It is so small that distinctly different degrees of density or velocity could scarcely occur upon it, because the positions of greatest and least density, of greatest positive and nega- tive velocity, are always separated by half the length of a wave. The ear is therefore in nearly the same condition as the eye would be if it looked at one point of the surface of the water, through a long narrow tube, which would permit of ^ seeing its rising and falling, and were then required to undertake an analysis of the compound waves. It is easily seen that the eye would, in most cases, completely fail in the solution of such a problem. The ear is not in a condition to discover how the air is moving at distant spots, Avhether the waves which strike it are spherical or plane, whether they interlock in one or more circles, or in what direction they are advancing. The cii'cumstances on which the eye chiefly depends for foi'ming a judgment, are all absent for the ear. If, then, notwithstanding all these difficulties, the ear is capable of distin- guishing musical tones arising from different sources — and it really shows a marvellous readiness in so doing— it must employ means and possess properties altogether difterent from those employed or possessed by the eye. But whatever these means may be — and we shall endeavour to determine them hereafter — it is clear that the analysis of a composite mass of musical tones must in the first place be closely connected with some determinate properties of the motion of the ^ air, capable of impressing theniselves even on such a very minute mass of air as that contained in the aural passage. If the motions of the particles of air in this passage are the same on two different occasions, the ear will receive the same sensation, whatever be the origin of those motions, whether they spring from one or several sources. We have already explained that the mass of air which sets the tympanic membrane of the ear in motion, so far as the magnitudes here considered are concerned, must be looked upon as a single point in the surrounding atmosphere. Are there, then, any peculiarities in the motion of a single particle of air which would differ for a single musical tone, and for a combination of musical tones ? We have seen that for each single musical tone there is a corresponding periodical * [These are of course rather more than flue organ pipes. See Chap. Y. sect. 5, and twice the length of the corresponding open compare p. 26rf. — Trmislator.] 30 COMPOSITION OF SIMPLE WAVES. motion of the air, and that its pitch is determined by the length of the periodic time, but that the kind of motion during any one single period is perfectly arbitrary, and may indeed be infinitely various. If then the motion of the air lying in the aural passage is not periodic, or if at least its periodic time is not as short as that of an audible musical tone, this fact will distinguish it from any motion which belongs to a musical tone ; it must belong either to noises or to several simultaneous musicll tones. Of this kind are really the greater number of cases where the dif- ferent musical tones have been only accidentally combined, and are therefore not designedly framed into musical chords; nay, even where orchestral music is per- fornied, the method of tempered tuning which at present prevails, prevents an accurate fulfilment of the conditions under which alone the resulting motion of the air can be exactly periodic. Hence in the greater number of cases a want of periodicity in the motion might furnish a mark for distinguishing the presence ^ of a composite mass of musical tones. But a composite mass of musical tones may also give rise to a jmrely periodic motion of the air, namely, token all the musical tones which intermingle, have pitch numbers which are all multiples of one and the same old mimher, or which Fio. 11. comes to the same thing, when all these musical tones, so far as their pjitch is concerned, may he regarded as the upper partial tones of the same prime tone. It was mentioned in Chapter I. (p. 22a, h) that the pitch numbers of the upper partial tones are multiples of the pitch number of the prime tone. The meaning of this rule will be clear from a particular example. The curve A, fig. II, represents a pendular motion in the manner explained in Chap. I. (p. 21/^), as produced in the air of the aural passage by a tuning-fork in action. The horizontal lengths in the curves of fig. 11, consequently represent the passing time, and the vertical heights the corresponding displacements of the particles of air in the aural passage. Now suppose that \\ith the first simple tone to which the curve A corresponds, there is sounded a second simple tone, represented by the curve B, an Octave higher than the first. This condition requires that two vibrations of the curve B should be made in the same time as one vibration of the curve A. In A, the sections of the curve d„8 and 8 8i are perfectly equal and similar. The curve B is also divided into equal and similar sections e e and c ej by the points e, c, €,. We could cer- tainly halve each of the sections e e and c c„ and thus obtain equal and similar sections, each of which would then correspond to a single period of B. But by CHAP. II. COMPOSITION OF .SIMPLE WAVES. 31 taking sections consisting of two periods of B, we divide B into larger sections, each of which is of the same horizontal length, and hence corres])onds to the same duration of time, as the sections of A. If, then, both simple tones are heard at once, and the times of the points e and dj, € and 8, e, and S, coincide, the heights of the portions of the section of curve e e have to be [algebraically] added to heights of the section of curve