247 
1878.] The Phonograph. 
stand of the instrument, and provided with adjustments by 
which a steel pin projecting from its centre may be accu- 
rately set in the middle of the groove and at a proper depth ; 
and in front of the diaphragm a mouthpiece is fixed, very 
similar in form to that employed in Professor Bell’s tele- 
phone. 
From the above description it will be evident that if the 
diaphragm be set into vibration by sounds being uttered into 
the mouthpiece, the steel pin attached to it, partaking of 
that vibratory motion, will enter into greater or less depths 
into the groove on the cylinder, according as the amplitude 
of vibration of the diaphragm by which its motion is con- 
trolled be large or small. If, while this vibration is going 
on, the cylinder be rotated in its screwed bearing, the point 
of the pin will trace out a spiral undulating path of motion 
within the groove, the amplitude of whose waves will be 
equal to that of the vibrations of the diaphragm, their length 
and form being dependent upon the rapidity and character 
of the undulations of the metallic membrane combined with 
the surface speed of the cylinder. 
In order to obtain a permanent record of this wave-like 
path a sheet of ordinary tin-foil is fastened round the cylin- 
der, being secured in its place by brass caps, shown on the 
drawing; and, as the centre of the diaphragm is adjusted 
so as always to be opposite to the middle of the groove, 
which is bridged over by the tin-foil, it follows that the pin 
in vibrating with the diaphragm must indent the tin-foil, 
which, at any spot below it, is unsupported by the resisting 
surface of the cylinder, having nothing but a groove behind 
it, and as the cylinder is rotated a chain of indentations is 
produced, which is in every particular a record of the sounds 
which originated them. 
So far the apparatus is complete as an instrument for re- 
cording sounds, and as such is not superior to many of its 
predecessors, — such as the very beautiful logograph of Mr. 
W. H. Barlow, F.R.S., the phonautograph of M. Leon- 
Scott, or the instruments of Prof. Marey and the late Sir 
Charles Wheatstone,— but the most wonderful feature of 
Mr. Edison’s phonograph is that it not only interprets its 
own record, but does so by re-converting it into sonorous 
vibrations, repeating the sounds, whether articulate or other- 
wise, in the adtual voice in which they were originally com- 
municated to the mouthpiece. 
In Mr. Edison’s first apparatus this was accomplished by 
employing a second diaphragm of paper, fixed on the oppo- 
site side of the cylinder to the first diaphragm, and thrown 
