BOW SOUND AND WORDS ARE PRODUCED. 47 



1,100 feet in a second. Now, our A-fork, vibrating 440 times a second, 

 sets 440 sound-waves in motion in a second, so that, at the end of a 

 second, there would be 440 air-waves afloat, and the first one would 

 have reached a distance of 1,100 feet away. Now, there being 440 equal 

 air-waves in 1,100 feet, how far apart are they in other words, how 

 long is each wave ? Dividing the 1,100 feet by the 440 waves, we get 

 two and a half feet, or 30 inches, as the length of the air-waves of the 

 first A-tone above "middle C" the A-string of a violin. In the same 

 way we find that the first A of the bass of our piano produces air- waves 

 about forty feet in length, while the waves of the last A of the treble 

 are not quite four inches long. We find the length of the air- waves of 

 any musical note that is, the distance apart of the pushes in the air 

 by dividing 1,100 feet, the distance which the waves would cover in a 

 second, by the number of the note-vibrations per second, which repre- 

 sents the number of air-waves it would make in that time. 



One thing we notice in all sounds, and that is their character, or 

 peculiarity. They may be as near alike as they can be made, but 

 each different kind will have something about it which distinguishes it 

 from every other, and it is by this means that we distinguish different 

 instruments or voices. The cause of this is the peculiar shape in which 

 the wave comes from different sources, a sort of individual stamp by 

 which a sound carries the telltale mark of its maker. These different 

 stamps or trimmings of air-waves may be illustrated in Fig. 4, and will 



Fig. 4. 



be explained presently. The heavings represent the compressions, and 

 the hollows the rarefactions, in the air. Let A represent the wave-form 

 of the purely ideal tone of the note A with no stamp or quality given 

 to it. B might represent the wave-form given it by a piano ; and C, 

 that given to it by a violin. In each case the wave-length, or distance 

 between swells, and therefore pitch of tone, and the amplitude, or 

 size of swells, and therefore loudness of tone, are the same ; the only 

 difference is, that the last two tone-waves seem to be trimmed with 

 feather-waves, so to speak, the trimming varying with the source of 

 the wave. 



