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 denned 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 fashion: the vibrating body (a string for example) strikes the air-particles in its immediate vicinity, and they, being in con-
