FIG.

PAGE

49. Manometric Flames of Two Tubes of a Third

50.—Professor Blake's Method of Photographing Vibrations.

51.-Curve representing a Sound-wave.

98

99

111

57. The Flute. Longitudinal and Transversal Section of the Mouthpiece

172

ON SOUND.

INTRODUCTORY.

Sound, from a physical point of view, may be defined as Vibration appreciable to the ear. It appears, at its lower limit, to be continuous with vibration as detectable by ordinary tactile sensation; hence its exact musical commencement is rather indefinite. It is usually given at about thirty-two single, or sixteen double vibrations per second. Apparatus for the demonstration of this fact will be noted further on. Its higher limit is even more variable, owing to physiological differences between different ears; but 76,000 single, or 38,000 double vibrations probably represent the highest note ever heard.

The line of demarcation between mere noise and musical sound seems similarly vague. Dr. Haughton has ingeniously shown that the rattling of vehicles over equal-sized stones becomes musical at a definite velocity; from the confused rattle of a railway train in a tunnel the practised ear can disentangle, and, as it were mentally sift out, grand organharmonies; and a falling plank in the Crystal Palace gives musical notes by periodic repercussion at equal intervals. On the other side, castanets, tom-toms, side-drums, triangles, cymbals, all instruments of music proper, only give noise, similar to the guns added in Russia to Italian music, or the hundred anvils" 'played on" at the Boston Celebration. Even Beethoven, in his grandest symphony, sounds every note of the scale at once with musical effect. Helmholtz lays down the axiom that the sensation of musical sound is caused by rapid and periodic movements of the sonorous body, the sensation of noise by non-periodic movements.

The present text-book is concerned mainly with the instrumental appliances which minister to sound. The physical aspect of Acoustics has been lucidly mapped out by ClerkMaxwell in the following manner :—

VIBRATIONS AND WAVES.

Physical Aspect of Acoustics.

1. Sources-Vibrations of various bodies:

3. Pugging of floors, Dampers of Pianofortes.

4. Reservoirs, Resonators, Organ Pipes, Sounding-boards.

5. Regulators

6. Detectors

Organ Swell.

The Ear, Sensitive Flames,
Membranes, Phonautographs, &c.

7. Tuning-forks, Pitch-Pipes, Musical Scales.

To bridge over the gap between this science and the art of music, slightly more extended treatment is needed :

:

1. MODES OF PRODUCTION. VIBRATION OF SONOROUS BODIES. 2. MODES OF PROPAGATION. VELOCITY. WAVE-MOTION.

REFLECTION. REFRACTION.

3. INTENSITY. CONSONANCE.

INTERFERENCE.

4. PITCH. MODES OF DETERMINATION AND MEASUREMENT. STANDARDS OF PITCH.

5. NATURE OF MUSICAL TONE. QUALITY. RESULTANT TONES.

6. EFFECTS OF HEAT. ATMOSPHERIC PRESSURE. MOISTURE. DENSITY.

7. SCALES. TEMPERAMENT. TUNING.

8. THE EAR AND VOICE. SPECIAL APPLICATIONS TO MUSIC.

The whole subject naturally and more concisely divides itself into-1. Mechanical; 2. Theoretical considerations; 3. Practical applications. It is, however, to be noted that these different aspects of the facts cannot be separated one from the other; the respective influences of the art of music and of scientific research having been reciprocal, gradual, and intimately combined. At the very outset of history we meet with the Monochord, named after Pythagoras, a machine not intended for artistic performance, but which at once yielded immense practical results to music. We then enter into a long period during which instrumental appliances grew, without design and without theory. The discoveries of new or improved instruments were purely technical, often fortuitous; although every instrument added was a piece of mechanism open to scientific analysis. During the present century a return has been made to apparatus essentially scientific, for the explanation of what had been musically invented; we find soon the reciprocal influence of instruments on apparatus-no better instance of which can be given than the discovery of Tartini's “Terzo Suono," or third sound; originally taught by the great violinist to his pupils as a means of accurate tuning, but now shown by Helmholtz to involve a new and important acoustic principle.

In many cases instruments of music actually stand in the place of apparatus. Strictly considered, a musical note is of itself a mathematical fact, quite independent of its power of exciting emotion and pleasure by its artistic production. On the other hand, tuning and intonation, originally left entirely to the accurate and cultivated ear of a skilled performer, have become a branch of science, with definite laws and practical rules; insomuch that the unconscious departures from a fixed tuning, which older musicians made by a kind of instinct, are now explained; and even the disposition of various instruments, with different qualities of tone, in an orchestra is shown to be correct, or the contrary, according as the harmonics of each peculiar quality are consonant or dissonant.