82 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the value lay between these two extremes. The unexpected result 

 was also reached that the value of the maximum excursion was much 

 greater when both electrodes were of platinum than when both were 

 of carbon. It was least when the hammer was of platinum and the 

 anvil cf carbon. 



A series of observations was also made upon the microphone of the 

 Blake transmitter. These presented considerable difficulty ou account 

 of the construction of the parts of that instrument, and only a low 

 magnification could be used. Three sets of measurements were taken, 

 the first with a very light normal pressure, the second with the ordi- 

 nary pressure, and the third with a very heavy pressure. "With this 

 microphone in its proper condition, both electrodes moved. It was 

 therefore necessary to subtract the excursion of the anvil electrode 

 from that of the hammer, in order to obtain their relative motion. The 

 results reached are given in Table XX. The total excursion of the 

 hammer electrode, and its motion relative to the anvil, are given as 

 nearly as they could be measured. 



TABLE XX. 

 Blake Traksmitter. — Electrodes, Cahbox, PLAXixrir. 

 a. Light \ormaI Pressure. 

 Total Excnisioii. BelatiTe Excursion. Character of Sound. 



< 25 X 10-^ Gk>od quality, very faint. 

 50 X 10-^ 25 X 10-6 " " clear. 



100 X 10-« 50 X 10-5 Overtones strong. 



b. Medium Normal Pressure. 



< 25 X 10-6 Good quality, very faint. 

 75 X 10-6 25 X 10-« " " clear. 



100 X 10-6 50 X 10-6 Overtones strong. 



c. Heavy Xormal Pressure, 



< 25 X 10-6 Gx)od quality, very faint 

 100 X 10-6 25 X 10-6 « " clear. 



150 X 10-6 50 X 10-6 Overtones strong. 



These results, although of only approximate exactness, are interest- 

 ing, as they show one cause of the excellence of the Blake transmitter 

 in practice, in that the mode of support of the electrodes allows of 

 very considerable variations in the absolute motions of both of them 

 without material change in their relative motions. 



Rogers Laboratory of Physics, 

 March, 1890. 



