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On the Relative Velocities of Sound Waves of 

 Different Intensities. 



Arthur L. Foley, 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 found 

 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 Avhen the stations Avere 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." 1 

 But three changes have been made in the apparatus there shoAvn. One is the 

 short-circuiting of the capacity by a high resistance and inductance to giA'e 

 better regulation of the time interA r al betAveen the sound and illuminating 



Physical Review, Vol. XXXV, No. 5. Nov., 1912. 



