196 WELLS'S NATUKAL PHILOSOPHY. 



exists between two sounds, is the proportion between 

 their respective numbers of vibrations. 

 What is a 425. A combination of harmonious sounds 



Tihord, etc.? jg termed a musical chord; a succession of har- 

 monious notes, a melody; and a succession of chords, har- 

 mony. 



A melody can be perf)rmed, or executed by a single voice; a barmony 

 requires two or more voices at tlie same time. 



Define concord 426. Whcu two tones, or notes, sounded to- 

 and discord. gether produce an agreeable effect on the ear, 

 their combination is called a musical concord ; when the 

 effect is disagreeable, it is called a discord. 



Explain what ^'^'^ ' ^'^PP^'^'' '"'^ ^'^"^^ ^ Stretched string, as a wire or a 

 Is meant by the piece of catgut, such as is used for stringed instruments: now 

 of music.'^ ^"^^^^ *^^® number of vibrations which sucli a cord will make in a 

 given time, are inversely as its length ; that is, if the whole 

 cord makes a given number of vibrations in one second, as 100, on shortening 

 it one half it will make twice as many, or 200, and this will yield a note ex- 

 actly an octave higher than the former one. If we reduce its length three- 

 fourths, it will make four times as many "vibrations as at first, and yield a 

 note two octaves higher. 



Suppose the stretched string, or wire, to be 32 inches in length. When 

 this is struck it will viljrate a certain numl^er of times in a second, and give 

 what is called a key-note. Reduce the string one half, and we have the oc- 

 tave of that note. But between the key-note and its octave there is a natu- 

 ral gradation by intervals in the pitch of the tone, which heard in succession 

 are harmonious, the octave, as its name implies, being the eighth pitch of 

 tone, or eighth successive note ascending from the key-note. 



These eight notes, or intervals in the pitch of tone between the key-note 

 and its octave, constitute what is called the gamut, or diatonic scale of music, 

 because they are the steps bj^ which the tone natufallj'- ascends from any note 

 to the corresponding tone above, produced by vibrations twice as rapid. 

 These several notes are distinguished both by letters and names. They are: 

 C, D, E, F, G, A, B, C; 

 Or — do, re, me, fa, sol, la, si, do. 

 „ , They may also be distinguished by numbers indicating the 



notes of the length of the strings and the number of vibrations required 

 Bcale indicated? ^^ produce them. Thus, the length of the string producing 

 the primary, or key-note, being 32 inches, the lengths of the strings to produce 

 the tones in the entire scale are — 



32, 30, 27, 24, 21, 20, 18, IG; 

 or, supposing that whatever be the number of vibrations per second necessaiy 

 to produce the first note iu the scale, C, we agree to represent it by unity, 



