ON THE PHONOGRAPH. 769 



phragm. A hasty inspection of the more complicated apparatus in the English model 

 might lead one to suppose that the action in it was of the same nature, but a more 

 careful scrutiny will show that this is not the case. By the model now exhibited you 

 will see that, when pressure is made on the diaphragm, the effect is to cause the cutting 

 edge of the recording gouge to be directed downwards. As the cutting edge of the 

 gouge is directed against the wax cylinder and is opposed to the rotation of the latter, 

 it is evident that this change of the angle of the gouge to a downward direction will 

 cause the gouge to cut a deeper groove into the wax cylinder. The depth of the groove, 

 as determined by the angular movement, is therefore a measure of the pressure on the 

 glass disk. It must be borne in mind that when no pressure is exerted on the glass disk 

 the marker cuts a groove. When there is greater pressure, by the cutting edge being 

 placed at a larger angle with the tangent of the curved surface of the cylinder, a deeper 

 groove will be cut. On the other hand, when the cutting edge is placed at a smaller 

 angle with the tangent of the curved surface of the cvlinder a shallower groove will be 

 ploughed on the surface of the wax cylinder. It follows that, if the sound falling on the 

 wax cylinder of the phonograph be very intense, during the increase of pressure the 

 groove will be deep, and during the diminution of pressure the groove will be shallow ; 

 and so great may be the difference between the plus pressure of condensation and the 

 minus pressure of rarefaction that during the latter the recording point will only skim 

 the surface of the wax cylinder, without making any groove. This explains an anomaly 

 in several of the photographs taken of portions of the surface of the wax cylinder. For 

 example, a photograph of a portion of a record taken of sound emitted by a full organ 

 shows deep furrows, continued for a considerable distance, corresponding to the long 

 chord-like sounds of the instrument, and these are succeeded by portions in which there 

 is no groove. This is well seen in the fig. 1 (Plate I.). In this case, so great has 

 been the rebound from the state of great pressure that the cutting edge has only slid 

 along the surface of the wax cylinder without cutting a groove. The same is seen when 

 chords are made by bowing several strings of the violin, as in fig. 2 (Plate I.). 



10. It is possible that here we have the explanation of one of the imrjerfections of the 

 phonograph, or, perhaps, rather an illustration of the wrong way of using the instrument. 

 All who have tried the instrument must have observed that the best effects are obtained 

 by tones of moderate intensity. If too weak, the tones given out on reproduction are 

 only imperfectly heard on account of their weak intensity, and by no system of reinforce- 

 ment or electrical relays can these be made fairly audible. On the other hand, if too 

 strong, there are two risks : — (1st) The intensity of the tone may cause a jarring between 

 the end of the wire in the loop connecting the wire of the lever with the wire from the 

 glass disk, and, as this is communicated to the glass disk, a noise is produced ; and (2nd) 

 the intensity of the tone may be so great as to cause, during the rarefaction of the air 

 corresponding to the diminution of pressure, the recording marker to come to the surface 

 of the wax cylinder, or even to leave it altogether. Suppose the marker just skims the 

 surface, it will produce a friction sound which must affect quality, and suppose the 



