228 PROCEEDINGS OP THE AMERICAN ACADEMY 



XV. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XXIX.— EXPERIMENTS ON THE BLAKE MICRO- 

 PHONE CONTACT. 



By George W. Patterson, Jr. 



Presented by Charles R. Cross, January 11, 1888. 



In the spring of 1887, Mr. H. J. Tucker and I experimented on the 

 contact in the Blake microphone transmitter, with the object of de- 

 termining, if possible, the relation between the normal pressure at the 

 contact, and the current in the receiver of the telephone, which was 

 placed in the secondary circuit of an induction coil in the usual 

 manner. 



In the following pages I shall give a brief description of our ap- 

 paratus, and some account of our experiments, with the results reached ; 

 and in conclusion I shall deduce, from a consideration of the appara- 

 tus and the laws of electricity, equations for curves of pressure and 

 current which are similar to those obtained in experiment. 



In our laboratory work we had the advantage of a knowledge of 

 the work which had been done in the preceding two years by Messrs. 

 Page, Lewis, and Hopkins, under the direction of Professor Cross, 

 only a portion of which is published.* 



The object of our work being to determine the variations in the 

 secondary undulatory current caused by variations in the normal pres- 

 sure at the microphone contact, we required some simple way of regu- 

 lating the contact pressure, — some way, if possible, which would admit 

 of reproducing precisely the same results from the same conditions of 

 pressure and sound. This latter we failed to accomplish satisfactorily. 



Having removed the door, including the microphone contact and 

 the mouthpiece, from the transmitter, we fastened it to the table, 

 leaving space between it and the table for an organ pipe (512 com- 

 plete vibrations per second), which we used as our source of sound. 



* See Proc. Am. Acad., vol. xxi. p. 248. 



