MINIMUM INTENSITY OF SOUND 
91 
Fig. 17 
energy required to be given out from the source for audition with 
the direction of the observer making any angle x with the normal, 
Ex having different values at different angles ; or in other words, 
if Ex represented the different intensities at the source required to 
produce equal intensities at a constant distance but with different 
values for x, that the ratio of the intensity of sound passing out in 
different directions as given by x, when the energy leaving the 
source had a constant value Ec were proportional to 1/Ex. Figure 
16 gives the intensity flux in different directions from the dia- 
phragm as determined by this method. The intensity, in arbitrary 
units, is plotted as the ordinate, and the angle x as the abscissa. 
These results were obtained for a frequency of 12,800. The value 
of D was 600 cm. From the curve, R, for the direction of the 
observer normal to the diaphragm, was found to be about 50, and 
the value for E obtained was .65xlO~^ ergs. By this method the 
value of E was found for several other frequencies and the re- 
sults are given in Table 1. The column headed S in this table 
gives the sensitivity of the ear for the different frequencies where 
S is defined as 1/E. Figure 17 shows graphically the change in sen- 
sitivity of the ear with frequency. In order that it all might be 
shown on the same curve log S is plotted instead of S. 
