116 PROCEEDINGS OF THE AMERICAN ACADEMY. 



was repeated with the diaphragm of the telephone T at rest and silent. 

 The damping was effected usually by lightly pressing upon the dia- 

 phragm with the finger, but in some cases it was affected by inserting a 

 light wedge (a quill) between the diaphragm and pole, when this opera- 

 tion was permitted by an open structure telephone. The balance, 

 when the diaphragm was damped, gave practically complete silence in 

 the head-telephones H, and the settings of resistance and inductance 

 were consistent within about ^ of 1%. The balance, on the other 

 hand, when the diaphragm was in motion, was not so good. In this 

 case, difficulties were introduced by parasitic notes probably due to 

 currents of higher frequency generated by the motion of the telephone 

 diaphragm. It was usually possible, however, to balance out the 

 fundamental tone, with adjustments consistent within 1 or 2 ohms. 



III. Particulars of the Telephones Tested. 



Several telephones were submitted to measurements. Four of the 

 instruments, for which the results are presented in the present account, 

 were : — 



1. A Western Electric Bipolar Bell Telephone, Type 122, here 

 designated "Rb'j 



2. A Western Electric Bipolar Watch-case Telephone receiver, 

 designated "Watch-case," 



3. An experimental specially-constructed monopolar receiver, 

 here designated "Experimental monopolar," and 



4. An experimental bipolar telephone receiver, provided with 

 exploring coils, and here designated "Experimental bipolar." 



The following table (Table I) contains some of the mechanical 

 particulars of these instruments. 



IV. Experimental Data and Results. 



The data obtained by measurements of the resistance and inductance 

 of the first three of the above receivers are contained in Tables II to 

 VI. The data with the "experimental bipolar" receiver are not 

 tabulated, as they Avere taken for the specific purpose of determining 

 the angle of lag of magnetization of the iron behind the actuating 

 current and this subject is discussed later. 



Explanation of Tables. — A brief explanation of Table II, obtained 

 with the bipolar Bell "Rb" with 0.3 effective volts applied at its 

 terminals, will be given as typical of all the tables. The first column 



