actuated by Resistance-temperature Variations. 131 



current, and appears to be practically independent of the shape 

 of the galena surfaces at the contact. 



The experiments now to be described were made on selected 

 galena-galena combinations in precisely the same way as the 

 earlier experiments on the iron-oxide detectors. The diagram 

 of the apparatus employed is shown in fig. 1 of the previous 

 paper (Phil. Mag. June 1910, p. 872). The mutual in- 



ductance between L and 

 results described below. 



1/ was 2500 cm. in obtaining the 











Fig. 1 











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(b) 





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a) 



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1 



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A 





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i 

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 i 



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sti 



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0-2 



0-4 



06 0-8 



1-0 



1-2 



1-4 Volt 



The detector was placed at D and submitted to an electro- 

 motive force from P 2 , which was varied in steps from zero 

 to about one volt positive or negative. At each step an 

 observation was made of the steady current through the 

 detector, and of the intensity of the sound produced in the 

 telephone by electrical oscillations of amplitude fixed by the 

 position of the jockey on P^ The steady current observation 

 was made by means of a shunted galvanometer kept connected 

 in series with the telephone. The intensity of the sound was 

 measured by balancing the sound from the detector against 

 that from the interrupter and the potential-divider P 3 . Thus 



K2 



