OF ARTS AND SCIENCES. 233 



XVI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XXXVL — ON THE INFLUENCE OF THE STRENGTH 

 OF THE MAGNET IN A MAGNETO TELE- 

 PHONE RECEIVER. 



By Charles R. Cross and Harry E. Hayes. 



Presented November 12, 1890. 



The present investigation is a continuation of the research described 

 in a paper by Messrs. Cross and Williams, previously published in 

 these Proceedings (vol. xxiv. p. 113). With a magneto telephone 

 transmitter it was found that, as the strength of the magnet was in- 

 creased, the induced current produced by a definite motion of the dia- 

 phragm increased quite rapidly to a maximum, and then gradually 

 decreased. With diaphragms of different thickness it was found that, 

 as the field necessary to saturate the diaphragm increased in strength, 

 the maximum value of the induced current occurred with a greater 

 strength of field, and also that the value of this maximum current 

 increased with the thickness of the diaphragm, other things remaining 

 the same. One series of measurements, however, whose results are 

 shown in curve No. 23, Figure 2, of that article, seemed to be at va- 

 riance with this conclusion, a discrepancy which was explained on 

 the supposition that the supports holding the cam-rod by which the 

 diaphragm was thrust forward yielded to a material extent with the 

 thicker and stiflfer diaphragm, which, by lessening the motion of this, 

 would produce the observed result of a diminished current. 



A series of measurements was first made in order to ascertain 

 whether the above conclusion was correct. The apparatus employed 

 was identical with that described in the previous article referred to, 

 but the supports carrying the cam-rod were much increased in rigidity. 

 The same diaphragms were employed as in the earlier experiments. 

 The results were such as to show that the explanation of the dis- 

 crepancy suggested was the true one, as will be seen on an examination 

 of Tables I., II., and III. The diaphragms used were of iron, and of 



