If you cause the tongue of this little instrument to vibrate, it will
produce a very low sound; but if you place it before a cavity (as the
mouth) containing a column of air, which vibrates much faster, but
in the proportion of any simple multiple, it will then produce other
higher sounds, dependent upon the reciprocation of that portion of
the air. Now the bulk of air in the mouth can be altered in its form,
size, and other circumstances, so as to produce by reciprocation many
different sounds; and these are the sounds belonging to the Jew’s Harp.
A proof of this fact has been given by Mr. Eulenstein, who fitted into
a long metallic tube a piston, which being moved, could be made to
lengthen or shorten the efficient column of air within at pleasure. A
Jew’s Harp was then so fixed that it could be made to vibrate before
the mouth of the tube, and it was found that the column of air produced
a series of sounds, according as it was lengthened or shortened; a
sound being produced whenever the length of the column was such that
its vibrations were a multiple of those of the Jew’s Harp.