280 
IOWA ACADEMY OF SCIENCE 
Fig. 1 shows the sphere and tube mounted near the edge of the roof 
of the new Physics building about 75 feet above the ground and no 
other buildings within several hundred feet. The roof in the neighbor- 
hood of the apparatus was covered with % inch hair felt. The sphere 
was constructed of cement, the wall being about 5 cm. thick. The sound 
was produced by an eleetromagnetically operated C fork placed in a 
funnel from which the sound was conducted along the roof through a 
pipe 25 feet long to the vertical pipe shown in Fig. 1. A watersealed 
joint at L made it possible to rotate the sphere about a vertical axis, 
A set of observations was made by placing the sphere so that the open- 
ing was turned away from the Rayleigh disk tube, and then rotating 
it through 180 degrees until in the position shown in the figure, readings 
being taken for each 15 degrees. The results were then plotted as shown 
in figures 3 and 4, the curves indicating the theoretical values and the 
small circles the experimental results. These results are from single 
sets of observations and not the average of several. 
The chief sources of error in the experiment were the inconstancy of 
the tuning fork, the absorption of energy by the resonating tube, and 
air currents which tended to disturb the disk. It is quite possible that 
the experiment may be performed under more favorable conditions, 
giving even closer agreement between the experimental and theoretical 
values. 
The results already obtained seem to indicate that the Rayleigh disk 
may prove to be very useful apparatus in the determination of relative 
sound intensities. A more complete account of the experiment may be 
found in the Physical Review, Vol. 1, No. 4, April, 1913. 
