Part 24 (1/2)

[Ill.u.s.tration: TRIANGLE. Height, about 8 in.]

28. The _harp_ is one of the oldest of instruments (dating back over 6000 years), but it is only in comparatively recent years that it has been used in the symphony orchestra. Its range is from [Ill.u.s.tration: CC-flat] to [Ill.u.s.tration: f-flat”'].

[Ill.u.s.tration: HARP. Height, 5 ft. 8 in.]

The modern _double-action harp_ has forty-six strings, which are tuned in half-steps and whole-steps so as to sound the scale of C[flat] major.

It has a series of seven pedals around its base, each pedal having two _notches_ below it, into either of which the pedal may be lowered and held fast. The first pedal shortens the F[flat] string so that it now sounds F, (giving the key of G[flat]); the second one shortens the C[flat] string so that it sounds C (giving the key of D[flat]); the third pedal shortens the G[flat] string so that it sounds G (giving the key of A[flat]); the fourth changes D[flat] to D (giving the key of E[flat]), and so on until, when all the pedals are fixed in their first notches, the scale of C is sounded instead of C[flat] as was the case before any of the pedals were depressed. But if the first pedal is now pushed down into the second notch the original F[flat] string is still further shortened and now sounds the pitch F[sharp] (giving us the key of G), and if all the other pedals are likewise successively lowered to the second notch we get in turn all the _sharp keys_--D, A, E, B, F[sharp] and C[sharp], the last-named key being obtained as the result of having all the pedals fixed in their second notches, thus making all the tones of the original C[flat] scale a whole-step higher so that they now sound the C[sharp] scale.

Chords of not more than four tones for each hand may be played simultaneously on the harp, but arpeggio and scale pa.s.sages are the rule, and are more successful than simultaneous chords. The notation of harp music is essentially like that of piano music.

APPENDIX C

ACOUSTICS

NOTE:--It is usually taken for granted that the student of music is familiar with the significance of such terms as _over-tone_, _equal temperament_, etc., and with principles such as that relating to the relation between vibration rates and pitches: the writer has in his own experience found, however, that most students are not at all familiar with such data, and this appendix is therefore added in the hope that a few facts at least regarding the laws of sound may be brought to the attention of some who would otherwise remain in entire ignorance of the subject.

1. _Acoustics_ is the science which deals with sound and the laws of its production and transmission. Since all sound is caused by vibration, _acoustics_ may be defined as the science which treats of the phenomena of sound-producing vibration.

2. All sound (as stated above) is produced by vibration of some sort: strike a tuning-fork against the top of a table and _see_ the vibrations which cause the tone, or, if the fork is a small one and the vibrations cannot be seen, hold it against the edge of a sheet of paper and hear the blows it strikes; or, watch one of the lowest strings of the piano after striking the key a sharp blow; or, look closely at the heavier strings of the violin (or better still, the cello) and watch them oscillate rapidly to and fro as the bow moves across them.

The vibrating body may be a string, a thin piece of wood, a piece of metal, a membrane (cf. drum), the lips (cf. playing the cornet), the vocal cords, etc. Often it is a column of air whose vibrations give rise to the tone, the reed or other medium merely serving to set the air in vibration.

3. Sound is _transmitted_ through the air in somewhat this fas.h.i.+on: the vibrating body (a string for example) strikes the air-particles in its immediate vicinity, and they, being in contact with other such air-particles, strike these others, the latter in turn striking yet others, and so on, both a forward and backward movement being set up (oscillation). These particles lie so close together that no movement at all can be detected, and it is only when the disturbance finally reaches the air-particles that are in contact with the ear-drum that any effect is evident.

This phenomenon of sound-transmission may perhaps be made more clear by the old ill.u.s.tration of a series of eight billiard b.a.l.l.s in a row on a table: if the first ball is tapped lightly, striking gently against ball number 2, the latter (as well as numbers 3, 4, 5, 6, and 7) will not apparently move at all, but ball number 8 at the other end will roll away. The air-particles act upon each other in much this same fas.h.i.+on, the difference being that when they are set in motion by a vibrating body a complete vibration backward and forward causes a similar _backward and forward_ movement of the particles (oscillation) instead of simply a _forward jerk_ as in the case of the billiard b.a.l.l.s.

Another way of describing the same process is this: the vibration of some body produces waves in the air (cf. waves in the ocean, which carry water forward but do not themselves move on continuously), these waves spread out spherically (i.e. in all directions) and finally reach the ear, where they set the ear-drum in vibration, thus sending certain sound-stimuli to the nerves of hearing in the inner ear, and thus to the brain.

An important thing to be noted in connection with sound-transmission is that sound will not travel in a vacuum: some kind of a medium is essential for its transmission. This medium may be air, water, a bar of iron or steel, the earth, etc.

4. The _rate_ at which sound travels through the air is about 1100 feet per second, the rapidity varying somewhat with fluctuations in temperature and humidity. In water the rate is much higher than in air (about four times as great) while the velocity of sound through other mediums (as _e.g._, steel) is sometimes as much as sixteen times as great as through air.

5. Sound, like light, may be _intensified_ by a suitable reflecting surface directly back of the vibrating body (cf. sounding board); it may also be reflected by some surface at a distance from its source in such a way that at a certain point (the focus) the sound may be very clearly heard, but at other places, even those _nearer_ the source of sound, it can scarcely be heard at all. If there is such a surface in an auditorium (as often occurs) there will be a certain point where everything can be heard very easily, but in the rest of the room it may be very difficult to understand what is being said or sung.

_Echoes_ are caused by sound-reflection, the distance of the reflecting surface from the vibrating body determining the number of syllables that will be echoed.

The _acoustics_ of an auditorium (_i.e._, its hearing properties) depend upon the position and nature of the reflecting surfaces and also upon the length of time a sound persists after the vibrating body has stopped. If it persists longer than 2-1/4 or 2-1/3 seconds the room will not be suitable for musical performances because of the mixture of persisting tones with following ones, this causing a blurred effect somewhat like that obtained by playing a series of unrelated chords on the piano while the damper-pedal is held down. The duration of the reverberation depends upon the size and height of the room, material of floor and walls, furniture, size of audience, etc.

6. Sound may be cla.s.sified roughly into _tones_ and _noises_ although the line of cleavage is not always sharply drawn. If I throw stones at the side of a barn, sounds are produced, but they are caused by irregular vibrations of an irregularly constructed surface and are referred to as _noise_. But if I tap the head of a kettle-drum, a regular series of vibrations is set up and the resulting sound is referred to as _tone_. In general the material of music consists of tones, but for special effects certain noises are also utilized (cf.

castanets, etc.).

7. Musical tones have three properties, viz.:

1. Pitch.

2. Intensity.