THE HAMILTON ASSOCIATION. 45 
While speaking of the organ we will next take up the ‘‘reed ” 
section—that is, the starting of the vibrations by the action of reeds 
or metal tongues. - To describe this, take (in fancy) a small reed or 
pipe; shave off one side of the stopped end until an aperture is 
made; put a tongue of thin wood or metal over this opening and 
fasten it to the end farthest from the end of the pipe. If you try to 
blow into the end the air will have difficulty in getting through the 
aperture, and the spring of the tongue will start a vibration which 
will produce a note determined by the number of vibrations made. 
If the tongue is wide enough to lie on the edges of the aperture it 
is called a ‘‘striking reed,” if it is narrow enough to pass through 
to and fro it is called a ‘‘free reed.” Most organ reeds are striking 
reeds, as the clarionet, oboe and horn. The orchestral oboe and 
bassoon are on a somewhat different principle, or rather different 
adaptation of the same principle. The entrance to the pipe is 
almost filled up by two thin tongues (called reeds) which meet 
together and spring apart again under the infiuence of the current 
of air which is striving to enter the pipe. In all the cases men- 
tioned the vibrations started would have very little effect if they 
were not caught in a tube or sound-box of some kind, so as to be 
amplified before being transmitted to the surrounding atmosphere. 
We will now consider the starting of sound by means of a 
stretched string or wire. If a wire is stretched tightly between two 
points it will, if disturbed, start a vibratory motion that will gradu- 
ally diminish until it returns to rest. The number of vibrations 
will depend on the length of string, its thickness, and the tightness 
with which it is stretched. When it is tight enough to make sixteen 
or more vibrations per second, it becomes a musical note. It will, 
however, make but little sound unless it has a sound-board or 
resonance chamber in connection with it. The same applies to the 
tuning fork, which forms tone by vibrations of the prongs, and is 
barely heard until the base of the fork is applied to a sound-box of 
some kind. 
Several interesting and instructive experiments can be made by 
the aid of the machine called the Siren, which help to establish 
many facts in connection with sound and its action. Imagine a 
pipe conveying a current of air or steam ; this pipe is opposed to the 
flat surface of a disk (metal, wood or cardboard) which revolves on 
