ON THE PHONOGRAPH. 773 



value of a given length of surface is accurately fixed. The photographic method, how- 

 ever, interesting as it may be, is not of great value, as it does not give the forms of the 

 curves represented by the bottoms of the depressions made by each vibration of the disk 

 of the phonograph. 



C. Mechanical Tracing of the Curves. 



16. A mechanical representation of the curves presents many difficulties. These 

 were so far overcome by the device of Jenkin and Ewing with the tinfoil phonograph. 

 The method followed by these observers, which was entirely mechanical, was to cause 

 the disk of the phonograph to record its movements on a drum moved at the same rate 

 as that of the cylinder. As already mentioned, Hermann photographed the oscillations 

 of a beam of light reflected from a small mirror connected with the disk of the phono- 

 graph, the whole apparatus moving slowly. My method consisted in the adaptation of a 

 light lever to a marker connected with the phonograph itself, and so arranged that it (the 

 point of the marker) would travel over all the ups and downs of the phonographic curve 

 on the wax cylinder at an extremely slow rate. The obvious objections to any method 

 of directly recording the ups and downs of the lever is that the inertia of the lever 

 might cause extraneous vibrations, while at the same time the smaller marks on the wax 

 cylinder might be missed. These objections, however, may be removed by (a) reducing 

 friction to a minimum, and (b) moving the phonograph cylinder so slowly as to make 

 the movement almost invisible to the naked eye. In this way inertia ceases to be a 

 trouble. 



17. After various attempts with simple appliances, the apparatus shown in Plate I. 

 was fitted up, and by means of it the taking of curves became comparatively easy.* In 

 fig. 16, Plate I., a diagram of the arrangement is shown as simply as possible. The 

 first apparatus used was not specially made for the experiment, but consisted of fittings 

 in my own laboratory. The motive power for driving the apparatus is a small water 

 motor acting on a wooden wheel. From this wheel two trains of wheels or pulleys pass, 

 the one set, namely, 2, 3, 4, and 5', being gradually geared down so as to drive the 

 cylinder of the phonograph, 6,t at an extremely slow rate, and the other set, namely, 2', 

 3', and 4', to drive at a slow rate the recording drum a. By this arrangement the rate 

 of rotation of the cylinder of the phonograph is about once in five or six minutes, in- 

 stead of being once in one-half second, the usual speed in recording. The drum, a, also 

 moves very slowly, but a little faster (not twice as fast) than the cylinder of the phono- 

 graph, the object being to open out the curves somewhat in a linear direction. By 

 attaching an electric arrangement to the axle of the mandril carrying the phonograph 

 cylinder, 6, the time of each revolution of the phonograph cylinder was registered on 



* This apparatus has already been described in a short paper written for the Journal of Anatomy and 

 Physiology, vol. xxix. 



t The cord passes over (b), the wheel seen on the left end of the phonograph spindle in the figure show- 

 ing the instrument. The wheel will be recognised by a tape band passing vertically over it. 



VOL. XXXVIII. PART IV. (NO. 22). 5 P 



