OF ARTS AND SCIENCES. 265 



XXI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



VIII. — AN EXPERIMENTAL PROOF OF THE LAW OF INVERSE 

 SQUARES FOR SOUND. 



By William W. Jacqdes. 



Presented, May 10, 1876. 



Tpiere is every dynamical reason for believing that the intensities 

 of light, heat, and sound, diminish as the reciprocals of the squares 

 of the distances from their origins. 



That this is true of light and heat has been demonstrated experi- 

 mentally. The case of sound, however, has only been put to the test 

 in experiments so crude as not at all to warrant the assumption of the 

 law on experimental grounds. 



The following method (which was suggested by the reading of Pro- 

 fessor Mayer's paper in the ''American Journal" for January, 1873) 

 ranks in its degree of accuracy with those which have been applied to 

 the verification of this law in the cases of light and heat. It depends, ' 

 primarily, on the principle, that, when a particle of air is solicited by 

 two equal and opposite forces, it will remain at rest. 



If two resonators, adjusted so as to resound with equal intensity, be 

 placed equally distant from an organ-pipe, and connected by tubes 

 with the two prongs of a fork-shaped tube in such a way that the 

 sound-wave from one resonator shall arrive at the fork in opposite 

 phase to that from the other, we shall have this condition ; and, if the 

 stem of the fork be placed in the ear, no sound will be heard. If, in 

 place of one of these resonators, we put two, each of the same inten- 

 sity as the first, both connected with the same prong of the fork, we 

 may, by moving them farther from the source of sound than was the 

 single resonator, at the same time altering the length of the tubing so 

 that the wave from the single one shall arrive at the fork in opposite 

 phase to that from the pair, produce the same effect of complete inter- 

 ference. If the law of inverse squares holds true, the distances of the 

 sinsle resonator from the source of sound should be to the cor- 



