96 



PROCEEDINGS OF THE AMERICAN ACADEMY 



fixed amount, depending upon the magnitude of the current. Some 

 measurements were made which show the amount of this deflection 

 with increasing values of the magnetizing current. The results of 

 these are given in Table I. The current is given in milliamperes, the 

 deflection in thousandths of a millimeter. 



We did not carry the increase of current to a higher value, since 

 the deflection of the diaphragm would have become so great as to 

 carry the style out of the field of view. 



A comparison of these results — best seen by plotting them as a 

 curve, which we have not thought it necessary to reproduce here — 

 shows that on increasing the magnetizing current the corresponding 

 permanent deflection increases more and more rapidly in proportion 

 up to a value of about ^ of an ampere, after which the deflection is 

 very closely proportional to the current. 



In studying the effect of different degrees of magnetization of the 

 core of the receiver upon the amplitude of the vibration of the dia- 

 phragm, our mode of procedure was to pass a known direct current 

 through the magnetizing coil, and to vary the alternating line current 

 through the receiving telephone coil, measuring this current by the 

 electro-dynamometer. The extent of the excursion of the diaphragm 

 for each different current was measured by the spider-line micrometer. 

 The deflections given in the tables are each the mean of five readings. 

 The process described was followed for various values of the magnetiz- 

 ing current, with the results shown in Table II. The figures in the 

 first vertical column indicate the serial number of the measurements ; 

 those in the second, the strength of the magnetizing current in milli- 

 amperes, to which the strength of the magnet was found to be propor- 



