he chief property of the telephone?

(4.) The interposition of a plate of any substance whatever between the
diaphragm and the source of the vibratory motions in nowise alters the
telephonic qualities of the diaphragm, and consequently the _nature_ of
the motions that it effects--a fact that would be very astonishing if the
motions were those that corresponded to the peculiar sounds of the
diaphragm. This fact is already known, and I have verified it with mica,
glass, zinc, copper, cork, wood, paper, cotton, a feather, soft wax,
sand, and water, even in taking thicknesses of from 5 to 8 inches of
these substances.

(5.) We can put a diaphragm manifestly out of condition to effect its
peculiar scale of harmonics by placing small, unequal, and irregularly
distributed bodies upon its surface, by cutting it out in the form of a
wheel, and by punching a sufficient number of holes in it to reduce it
half in bulk. None of these modifications removes its telephonic
qualities.

(6.) We can go still further, and employ diaphragms of scarcely any
stiffness and elasticity without altering their essential telephonic
properties, the reproduction of a continuous series of sounds, accords,
and timbres. Such is the case with a sheet iron diaphragm. It is very
difficult, then, to imagine a fundamental sound and its harmonics.

The conclusion from all this appears to me to be that the mechanism by
virtue of which telephone diaphragms perform their motions is at least
analogous to, if not identical with, that through which solid bodies of
any form whatever (a wall, for example) transmit to all of their surfaces
all the simple or complex successive or simultaneous vibratory motions,
of periods varying in a continuous or discontinuous manner, that are
produced in the air in contact with the other surface. In a word, we have
here a phenomenon of _resonance_. In diaphragms of sufficient thickness
this kind of motion would exist alone. In thin diaphragms the motions
that correspond to their special sounds might become superposed upon the
preceding, and this would be prejudicial rather than useful, since, in
such a case, if there resulted a re-enforcement of the effects produced,
it would be at the expense of the reproduction of the timbre, the
harmonics of the diaphragm being capable of coinciding only through the
merest accident with those of the sounds that were setting in play the
fundamental sound of the diaphragm. This is what experimen