OF ARTS AND SCIENCES. 93 



VI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XL. —AN INVESTIGATION OF THE EXCURSION OF 

 THE DIAPHRAGM OF A TELEPHONE RECEIVER. 



By Charles R. Cross and Arthur N. Mansfield. 



Presented May 24, 1892. 



In a paper published in these Proceedings,* by Messrs. C. R. Cross 

 and H. E. Hayes, it was shown that with a magneto-telephone 

 receiver the magnitude of the change in the strength of the magnet 

 when a weak current is sent through the coil increases up to a certain 

 limit as the strength of the magnet is increased, and then diminishes, 

 the explanation of this diminution being found in the approach of the 

 diaphragm toward saturation. The effect of varying the thickness ol 

 the diaphragm upon the magnitude of this change was also studied, 

 and it was found that within the limits of the experiments the changed 

 strength of the magnet due to the weak current is greater with thin 

 than with thick diaphragms. 



From these results it would naturally be inferred (1) that the am- 

 plitude of the vibration of the diaphragm of a telephone receiver would 

 at first increase to a maximum, and then diminish, if the strength of 

 the magnet were continually increased; and (2) that, within such 

 rano-e of thickness of diaphragm as would probably be most Buitable 

 in practice, a thin diaphragm is preferable to a thicker one. 



The subject has also been studied by Mercadier,t by ascertaining 

 the distance at which the beat of a metronome, when transmitted by 

 telephone, just ceased to be audible under different conditions of the 

 receiver as to the thickness of the diaphragm and Btrength <»f the po- 

 larizing magnet. In Mercadier's experiments the thickness of the 

 diaphragms was varied through a far greater range than in tl 



* Vol. XXV. p. 233, 1890. 



t Comptes Rendus, 1889, Vol. CVIII. pp. 735, 797 ; 1891, Vol CXI1 | 



