454 Tufts — Transmission of Sound through Solid Walls. 



In all of the experiments above described the source of 

 sound, as has been stated, was a single pulse obtained by 

 dropping a metal ball on a pine board. Some of the 

 experiments were repeated using an organ pipe as the source 

 of sound. In this case it was found that the results might be 

 much influenced by the pitch of the note used. If the natural 

 period of vibration of a disc was in unison with the source of 

 sound, while that of another less rigid disc was not, the 

 transmission might be greater through the more rigid disc. 



In conclusion, it may be stated that the experiments described 

 above are representative of many others of a similar character. 

 In every case the rigidity of the disc was found to be the 

 main factor in determining the intensity of the sound trans- 

 mitted from the air on one side of the disc to the air on the 

 opposite side. The only other factor which seemed to have 

 an appreciable influence on the transmission of sound through 

 the disc was its mass. It was found that of two discs having 

 the same rigidity the one possessing the greatest mass was the 

 poorest conductor of sound. The effect of increasing the mass 

 of a disc is, however, many times smaller than the effect of 

 increasing its rigidity. 



The above experiments show that the commonly accepted 

 analogy between the transmission of sound and that of light 

 does not hold where the sound is transmitted from the air on 

 one side of a solid medium, through the medium, to the air 

 on the other side. In such cases it has been found that an 

 entirely different principle is involved, and that the transmis- 

 sion takes place as a to and fro vibration of the wall itself, and 

 not as an elastic wave traveling through it. 



Physical Laboratory of Columbia University, 

 New York City. 



