xx TABLE OF CONTENTS 



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CHAPTER XX. Hearing, Voice, and Speech . . . . . . ... 489 



First Section: Auditory Sensations 489 



1. Stimuli Appropriate for the Organ of Hearing 489 



A. Loudness 489 



B. Pitch 489 



C. Timbre . 491 



2. Transmission of Sound in the Ear 493 



A. The External Ear 494 



B. The Middle Ear 494 



3. Excitation of the Auditory Nerve 498 



A. The Resonators in the Cochlea 498 



B. Objections to the Resonator Theory 501 



Second Section: Physiology of Voice and Speech . . .'-'". . . . 502 



1. Action of the Laryngeal Muscles 502 



2. Voice Production . 504 



3. Registers of Voice . 504 



4. Elements of Speech . . .506 



A. Vowels . . . , 506 



B. Consonants 507 



CHAPTER XXL Vision . . . /. . , . . 508 



First Section: The Eye as an Optical Instrument 508 



1. The Optical Constants of the Eye 508 



2. Images upon the Retina . . - 513 



A. Direct and Indirect Vision 514 



B. The Light-perceiving Layer of the Retina 514 



C. Visual Angle and the Limits of Vision 517 



3. Static Refraction in the Eye 519 



4. Optical Defects of the Eye 520 



A. Transparency of the Media of the Eye 521 



B. Form of the Refracting Surfaces 522 



C. Astigmatism . . . . . 522 



D. The Angle between the Line of Vision and the Optical Axis . . 525 



E. Chromatic Aberration in the Eye . . 526 



F. Summary . ' . . .527 



5. The Iris. . ..'.-. . . 527 



6. Accommodation ..,.-. . . . . . . . 529 



A. Range of Accommodation . ''-. ' -.* . . . . . . . 529 



B. Mechanism of Accommodation 530 



Second Section: Excitation of the Retina and Visual Sensations . . . .536 



1. Light Rays 536 



2. The Phenomena of Excitation 537 



A. Fatigue and Recovery of the Visual Organ 539 



3. Sensations of Color 541 



A. Relations of the Properties of Light to the Different Constituents of the 



Retina 541 



B. Successive Color Induction 542 



C. Color Mixture 542 



D. On the Theory of Color 544 



E. Simultaneous Contrast . . 547 



