9A PHYSICS. 
different tightness. A string half the length of another, and of the same 
tension, vibrates twice as quickly, and the musical note produced by it has 
a fixed relation to that produced by the other. From this it will be | 
understood why a fiddler places his fingers up and down on the strings 
as he plays. The string can only vibrate as far as the point on which —~ 
he places his finger; by putting his finger on the string a good way up, 
he shortens the string, and a sharper sound is produced; thus, besides. 
having the range of the four strings, which give different notes from 
being stretched to a different tightness (the bass-string being also loaded 
with copper wire, to make it vibrate more slowly), he has a range of 
notes on each string, by means of shortening them to different lengths. 
Different notes are also obtained from pipes, according to their length. 
The sound produced by a pipe is due to the vibrations of the air in the 
pipe, which are caused by the shock communicated by blowing into it, 
or partly by the construction of a mouth-piece. The shorter the pipe, 
the greater is the shrillness of the note produced. Every one knows 
that the note of a large flute is soft and mellow, while that of a 
small one is shrill. In an organ, there is a pipe for every note, the 
different lengths being calculated with extreme care; while in a flute 
a similar effect is produced by opening and shutting holes along the 
length of the one pipe. Another system on which musical notes are 
produced is by placing a slender elastic plate over a slit or opening 
through which air is made to pass, by blowing, as in the musical toy 
of this description. The air causes the little pieces of steel to vibrate 
with great rapidity and thus produce a musical note. The human 
voice consists simply of musical notes produced by the vibration of two 
membranes at the top of the windpipe, with their free edges opposite each 
other, and a slit or opening left between them for the passage of the air 
by which they are vibrated. When a boy places a blade of grass between 
his thumbs, and, by blowing on the edge, produces a note by no means 
musical in one sense, the note is produced exactly on the principle of the 
human voice as produced by the larynx, being caused by the extremely 
rapid vibrations of the edge of the blade of grass. The voices of 
children and women are shriller than those of men, because the mem- 
branes of the larynx are shorter in.the former than in the latter, and 
thus produce sharper notes. 
