ON PROFESSOR BELl's ARTICULATING TELEPHONE. 185 



second as the other one, they differ in pitch by the interval called 

 in music an octave. A tuning fork, which vibrates 256 times in 

 one second, produces the standard or concert pitch for the C on 

 the added line below the treble staff -, and the C in the middle of 

 the treble staff, is caused by 512 vibrations per second. The 

 lowest audible continuous sound is due to 23 vibrations per second, 

 and the highest limit of audible sounds for man is about 38,000 

 vibrations per second. The range of a 7-octave pianoforte, F to 

 F, is from 42 to 5,460 vibrations per second. 



Sounds differ from each other not only in intensity and pitch 

 but also in another respect. No one can ever mistake the sound 

 of a violin or a horn for that of any other instrument, although 

 they may sound the same note, i.e., produce the same number of 

 vibrations per second, and no two persons have voices alike. This 

 difference in tone which enables us to identify an instrument by 

 its sound, or a friend by his voice, is called quality of tone, or 

 timlre. We are indebted to the great German physicist, 

 Helmholtz, for the explanation of this phenomenon. He showed 

 that a musical sound is very rarely a simple tone, but is made up 

 of several tones, sometimes as many as ten or even fifteen, varying 

 in intensity and pitch. The lowest sound, which is also the 

 strongest, is called the fundamental, and is the one referred to in 

 speaking of the pitch of a sound. The higher sounds that 

 accompany it are called overtones, and they are simple n:ialtiples of 

 the fundamental, i.e., are 2, 3, 4, &c., times the number of 

 vibrations of it. It has been clearly demonstrated that the 

 character or quality of a sound depends altogether upon the 

 number and intensity of the overtones associated with the 

 fundamental. 



To recapitulate. — Sounds vary (i) in intensity, according to the 

 amplitude of the vibrations ; (2) in pitch, according to the number 

 of vibrations in a unit of time j and (3) in timbre or quality, 

 according to the number of overtones associated with the funda- 

 mental note. We shall see presently how all these variations are 



