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On THE RELATIVE VELOCITIES OF SOUND WAVES OF 
DIFFERENT INTENSITIES. 
Artruur L. Foury, Head of the Department of Physics, Indiana University, 
Publication No. 42. 
It appears that the first determination of the velocity of sound that can 
lay claim to any accuracy was made by Cassini, Maraldi, and LaCaille, of the 
Paris Academy, in 1738. By noting the time interval between seeing the flash 
of a cannon and hearing the report, with different distances between gun and 
experimenter, they arrived at the conclusion that the velocity of sound is 
independent of the intensity. This conclusion seems to have been accepted 
for more than a century. In 1864 Regnault determined the velocity of sound 
by firing guns reciprocally and using an electrical device for recording the 
instant of firing the gun and the arrival of the sound vave at the distant sta- 
tion. He found a small difference, about six parts in three thousand, in the 
velocities measured when the stations were 1,280 meters apart and when they 
were 2,445 meters apart, the former being the greater. The difference he 
attributed to the fact that the average intensity of the sound when the sta- 
tions were nearest was much greater than when farthest apart, thus reach- 
ing the conclusion that the velocity of sound is a function of its intensity. 
Regnault’s conclusion accords with theory and with experimental results 
obtained by several later experimenters. Among these may be named Jacques 
at Watertown, Mass., 1879, who obtained velocities of 1,076 feet per second, 
and 1,267 feet per second, at points 20 feet and 80 feet respectively to the 
rear of a cannon fired with a charge of one and one-half pounds of powder. 
Wolfe and others have found varying velocities for explosion waves, a wave 
from an electric spark being of this nature. A fuller consideration of these 
experiments will be given when the writer has completed his experimental 
work on this subject. 
The apparatus in use in this investigation, which is still in progress, is 
practically the same as described by the writer in a paper published three 
years ago under the title “A New Method of Photographing Sound Waves.” 
But three changes have been made in the apparatus there shown. One is the 
short-circuiting of the capacity by a high resistance and inductance to give 
better regulation of the time interval between the¥sound and illuminating 
, 
1Physical Review, Vol. XX XV, No. 5, Nov., 1912. 
