90 
IOWA ACADEMY OF SCIENCE Voi.. XXVIII, 1921 
sphere with a radius equal to the distance from the apparatus to 
the ear of the observer. However, since the sound does not pass 
out with equal intensity in every direction, this would only give 
the mean value of the flux of energy at that distance. In order 
to determine the actual value of E at the position of the observer 
(E being used to denote the number of ergs of sound energy flow- 
ing through a square centimeter per second for audition) one 
must multiply the mean value obtained by this method by some 
number R which gives the ratio of the intensity of the sound at the 
observer to the mean value of the flux taken over the whole sphere. 
Or one would have 
^ ASdA^ir^f^V ^ 
^ ~ AttD^ ^ 
where D is the distance between the observer and the tone gen- 
erator. 
The values of R for the frequencies used were found by sta- 
tioning the observer at a fixed distance from the tone generator 
and taking observations with different angles between the direc- 
tion from him to the source of sound and the normal to the dia- 
phragm of the instrument. The amplitude of the instrument was 
varied until the tone was just audible at each of these positions. 
It was assumed that if Ex represented the total amount of sound 
Fig. 16 
