Audibility Factor of a Shunted Telephone. 185 



From the two papers o£ Austin * it is not quite clear how 

 this calibration was made, and Hogan f assumes that his 

 " audibility factor " 



A - R+S 



where R is the resistance of the telephone, is proportional to 

 the square of the antenna current f . 



It was suggested to me by Dr. W. H. Eccles that this 

 point could be experimentally examined in the laboratory. 

 Dr. J. A. Fleming, F.R.S., thereupon kindly placed at my 

 disposal the means for doing this in the research department 

 of the Pender Electrical Laboratory of University College, 

 London. The following is a short account of the experiments 

 so far conducted. 



To generate high frequency oscillations of a steady 

 character a double Fleming and Clinton commutator J, 



Figr. 1, 



D , E 



A 



s 



mounted on the same shaft, was used. This commutator, 

 though originally designed for measuring small capacities, 

 but now connected in the circuits as shown in fig. 1, was 



* See papers cited. 



t See papers cited, and also Love, Phil. Trans. Roy. Soc. Lond. 

 vol. ccxv. A, p. 128(1915). 



J J. A. Fleming, ' Principles of Electric Wave Telegraphy and 

 Telephonv,' 3rd ed., p. 205. 



PMLMag. S. 6. Vol. 34. No. 201. Sept. 1917. 



