OF ARTS AND SCIENCES. 243 



The following approximate values were found from constructions of 

 the curves on a large scale. 



For No. 26, Maximum Current = 142, Field = .18 



" « 23, " " 137 " .13 



" " 22, " " 132 " .10 



" " 21, " " 131 " .06 



It also appears that with the thinner diaphragms the decrease of the 

 induced current with increase of field, after the maximum value of the 

 current is reached, is more rapid than with the thicker ones. More- 

 over, the deviation of the latter portion of the curve from a straight 

 line is greater in the case of the thinner diaphragms. 



The greater value of the maximum induced current with the thin 

 than with the thick diaphragm would naturally be ascribed to the less 

 stiffness of the former, and its consequent greater motion when a cur- 

 rent passes through the line, although its smaller mass and greater 

 ease of saturation must in a measure counterbalance this effect. The 

 quicker approach of the thin diaphragm towards saturation will ex- 

 plain the more rapid falling off of the current with it, and also the less 

 uniform rate of this change as the field increases. Curves 3, 4, 5, 6, 

 showing the effect of the diaphragm, still further illustrate these facts. 



It should be observed that the results which we have described do 

 not necessarily show the varying acoustic effect of the receiver, since 

 the amplitude of the motion of the diaphragm rather than the simple 

 amount of the change of strength of the magnet determines the mag- 

 nitude of the resulting air-waves, — at least according to the view 

 commonly held. We hope to return to the study of this part of the 

 problem, which is rendered somewhat dlflBcult on account of the very 

 small motion of the diaphragm. 



EoGERS Laboratory op Physics, 

 October, 1890. 



