ON PHYSIOLOGICAL APPLICATIONS OF THE PHONOGRAPH. 671 
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 rare- 
faction that during the latter the recording point may 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. 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. ' 
Tt is possible that here we have the explanation of one of the imperfec- 
tions 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 by reproduction are only 
imperfectly heard on account of their weak intensity, and by no system of 
reinforcement or electrical relays can these be made fairly audible. On 
the other hand, if too strong, there are two risks :—(lst) 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 marker leaves 
the surface altogether for a fraction of a second, there will be a rebound 
from the glass disk (owing to the removal of pressure coming from the 
marker) which is not exactly the same as the diminution of pressure due 
to the rarefaction of the aérial wave in the immediately preceding vibration 
These changes must affect quality of tone. 
3. The Committee has also been engaged on a method of recording 
variations in the intensity of the sounds of the phonograph. Suppose a 
series of sound waves of gradually increasing intensity to act on the disk 
of the phonograph, the pressure on the disk will gradually increase, and 
the normal groove will be cut deeper. In this process each vibration wil. 
be a little deeper than the one immediately before it, but the difference in 
depth will be very small. If the increase of pressure of the note or chord 
lasted more than half a second, the extent of surface covered by the 
recording point during that time would be nearly 7 inches, and there 
might be from 500 to 1,000 depressions in that distance. Suppose, now, 
that we recorded all these little depressions, it will be evident that the 
_ gradually increasing differences in height of the little curves would 
scarcely be appreciable. The slow method of recording vibrations, there- 
fore, whilst it is the method by which data can be obtained that have to 
do with pitch and quality, will fail in giving us a record of variations in 
intensity. This aspect of the matter came under notice at an early period 
of the investigation. So far as the Committee are aware, no one has 
attacked this side of the problem. Nothing is more striking in listening 
to the phonograph when it is reproducing either human speech or musical 
