July i, 1897J 



NATURE 



209 



THE ANAL YSIS OF PHONOGRAPH 

 RECORDS} 

 A FTER describing the general characters of waves, as regards 

 -^ pitch, amplitude, and form, Dr. McKendrick said :— 



Thus we can now understand what is meant by a compound 

 wave, and you will appreciate the statement that compound 

 waves may be very complex in character. If you look at the 

 curves showing the resultant waves, you will see that they repre- 

 sent, in a way, the character of the variations of pressure made 

 on the drum-head. With simple pendular waves, the drum-head 

 moves out and in with perfect regularity, like the movements of 

 a pendulum. The physiological effect of such simple pendular 

 vibrations is a sensation of a pure tone, such as you hear when I 

 Ixjw this tuning-fork. But if a compound wave falls on the 

 drum-head, it is not so easy to follow with the imagination the 

 variations of pressure. While these variations occur in regularly 

 recurring intervals of time so as to give the sensation of the pitch 

 of the fundamental tone, the movement may not be uniform on 

 each side of the median line, indicating the position of repose of 

 the drum-head, like the swing of a pendulum. Thus the drum- 

 head may move in, owing to the increase of pressure, faster 

 than it moves out, or the reverse ; or it may move in a little 

 distance, then return again to the starting-point and again move 

 in, and it may return to the position of rest after one or more 

 loand-fro movements Again, it may be pushed in to the 

 maximum distance, and remain in that position for a short time, 

 and then return to the original place of repose. Thus the 

 characters of the variations of pressure may vary to a remarkable 

 degree — to a degree, with a very complex sound, that is to us 

 almost inconceivable ; but we may be sure that these variations 

 of pressure will be faithfully followed by the drum-head, and 

 communicated by it to the deeper ear. When a compound wave 

 thus falls on the ear, the result is a sensation of sound of a 

 certain quality, or timbre, or clang, and we say that we hear the 

 sound of various musical instruments, as in a brass band or an 

 orchestra, or the sound of a particular instrument, a trombone, 

 a flute, a harp, a clarionet, or the sound of a well-known voice 

 that we can distinguish from all others. 



He then described the attempts to record graphically the 

 vibrations of bodies emitting sound from the time of Thomas 

 Young down to 1874-75, when the phonograph was invented. 

 In 1878, Fleeming Jenkin and Ewing succeeded in obtaining 

 tracings of the records of vowel sounds on the tinfoil phonograph, 

 and the curves were submitted to harmonic analysis. Since that 

 time, the marks on the tinfoil of the first phonograph have been 

 scrutinised by Grutzner, Mayer, Graham Bell, Preece, and Lahr. 

 The imperfections of the tinfoil phonograph made progress 

 impossible for ten years (from 1878 to 1888), during which 

 time, however, Edison, Graham Bell, and others were 

 engaged in working out the mechanical details of the wax- 

 cylinder phonograph. The subject was then taken up by 

 Hermann, and he succeeded in obtaining photographs of the 

 vibrations of the vowel sounds, a beam of light reflected from a 

 small mirror attached to the vibrating disc of the phonograph 

 being allowed to fall on a sensitive plate while the phonograph 

 was slowly travelling. The curves thus obtained were very 

 beautiful. In 1891, Boeke, in a laborious microscopical research, 

 measured the transverse diameters of the depressions on the 

 wax cylinder at different depths, and from these measurements 

 calculated the depths of the curves. He then reconstructed the 

 curves on a large scale, and he also has been busily engaged in 

 the analysis of vowel curves. 



Recently also Pipping has traced and analysed the curves 

 obtained by a kind of phonautograph constructed on the type of 

 the drum-head of the ear, and R. J. Lloyd has written two 

 valuable papers on the interpretation of the tracings obtained by 

 Pipping and by Hermann. 



Dr. McKendrick exhibited one of the first phonographs made 

 in this country. It was constructed by the late Prof. Fleeming 

 Jenkin in 1876. It represents the instrument in its simplest form. 

 You observe how the drum travels from side to side as in the phon- 

 autograph. The drum has a deep spiral groove, the thread of 

 which corresponds to that of the spindle on which the drum 

 rotates, and it is covered with thin, soft tinfoil. The membrane 

 has fixed firmly to its centre a .stout little marker having a 

 chisel-shaped edge. When sound waves fall on the membrane 



J Abstract of the Science Lecture for 1896, delivered to the PhiI0s0phic.1l 

 Society of Glasgow on December 16, 1896, by John G. McKendrick, M.D., 

 F.R.S., Professor of Physiology, University of Gl.osgow. 



NO. 1444. VOL. 56] 



it vibrates, and as the drum is rotaterl, the edge of the needle 

 pushes in the tinfoil into the spiral groove, and it makes a series 

 of indentations corresponding to the variations of pressures pro- 

 duced by the sound waves. When the sound is reproduced, we 

 run the point of the needle over these indentations by turning 

 the drum, and the varying pressures on the needle point caused 

 by the indentations act on the membrane, and reproduce the 

 sound. Thus this simple mechanism records the nutnber of 

 vibrations, corresponding to pitch, the relative amplitude of the 

 vibrations, corresponding to intensity or loudness, and the form 

 of the vibrations which has reference to the quality of the 

 sound. 



Since this remarkable invention first appeared, the phono- 

 graph has been improved so as to make it now a valuable 

 scientific instrument. Many are too apt to think of it as an 

 amusing toy, or as an apparatus that will serve the practical 

 purpose of a shorthand writer. It is both amusing and practical, 

 but it is much more. It is now a scientific instrument worthy of 

 a place in physical and physiological laboratories beside other 

 instruments of scientific research, and those employed for 

 demonstration in teaching. It merits this position because it 

 makes it possible to study some of the phenomena of sound in a 

 manner otherwise unattainable. 



Since 1877 the phonograph has been immensely improved, 

 and we now have it in the form that you see before you. The 

 machine used in this country is so geared that the wax cylinder, 

 6g inches in circumference, makes two revolutions in one second, 

 while the spiral grooves described on the cylinder are i/2CX3 inch 

 apart. A spiraUine about 136 yards in length may be described 

 on the cylinder, and the recording or reproducing point travels 

 over this distance in about six minutes. 



I have also used the American model, now also before you, 

 which resembles in all essential particulars the one I have just 

 described, except that the grooves are i/ioo inch apart, instead 

 of i/2C» inch. 



The mechanism by which the glass disc or diaphragm com- 

 municates its movement is shown by means of the large model 

 now before you. When sound waves fall on the glass disc, the 

 latter is subjected to variations of pressure, as I have already 

 explained. From the centre of the glass disc there coines a rod 

 which passes to the end of a lever, and to this lever a counter- 

 poise is attached. The end of the lever carries a sapphire point 

 which, like a gouge, cuts a spiral groove on the surface of the 

 wax cylinder. When there is increased pressure on the disc, the 

 inclination of the edge of the gouge is directed downwards at 

 such an angle with the surface of the wax cylinder as to cut a 

 groove of a certain depth ; but when the pressure becomes less, 

 the angle is changed, the gouge cuts more in a horizontal direc- 

 tion, and the groove ploughed out is not so deep. Conse- 

 quently as with each vibration of sound we have, as I have , 

 already explained, increased pressure and diminished pressure, 

 a series of marks of an oblong form are made in the bottom of 

 the groove, each little mark corresponding to a vibration. The 

 number of such marks, therefore, in a given distance— which, 

 when the velocity of the movement is taken into account, repre- 

 sents a certain interval of time, say the one-fiftieth of a second — 

 corresponds to the pitch of the note ; the depth of the marks 

 corresponds to the intensity of the vibration ; and the form of 

 the marks to the form of the vibration. Again, suppose a note 

 is sung dimintieiido to crescendo, and again to dimiiitteiido, the 

 depth of the groove will vary according to the intensity, at first 

 shallow, gradually becoming deeper till the maximum depth has 

 been reached, and again becoming more and more shallow. 

 These marks, therefore, on the wax cylinder are the representa- 

 tions of the mechanical effects of the vibrations in all respects- 

 number (pitch), depth (intensity or loudness), form (quality). 

 It will Ije evident, therefore, that if we run over these rnarks 

 again with the reproducing point, the glass disc will again vibrate 

 to the impulses received" by the ups and downs on the cylinder 

 as to reproduce faithfully, but with diminished intensity, the 

 original sound. It is, therefore, an investigation of great interest 

 to study these marks, to reproduce them on such a scale as to 

 enable us to study their form, and to let us see the ups and 

 downs as we would do, suppose we could make a longitudinal 

 section along the bottom of the groove, and looked at the marks 

 sideways. 



Before we set ourselves to the study of these marks, let me 

 bring under your notice certain other branches of the investiga- 

 tion. In the first place, we may, to a wonderful extent, increase 

 the volume of tone or loudness of the phonograph by the use of 



