1251 



By means of the binocular niicroscope M the place of contact could 

 be examined. This figure also shows that by means of the copper- 

 wire 1», the detector could l)e brought into contact with the Wnlf- 

 electrometer E. In order to know to what voltage the displacement 

 of string corresponded, the electrometer was connected to the poten- 

 tiometer P, by replacing 5, by the w-shaped /j^, thus connecting 

 the mercury cups 1 and 3. After the electrometei- had again obtained 

 the same deflection, the voltage was read from the voltameter. More- 

 over the contact could be tested as a detector. To this end electric 

 oscillations were excited in the system /Sj and induced into the system 

 S^. By removing 13 and making the contact A, the detector was 

 brought into the system S^ having a telephone 7'. Its action 

 as a detector was judged by the intensity of sound in the 

 telephone. 



§ 5. Characteristics of electrolytic detectors. 



The characteristic of the electrolytic detector distinctly shows that 

 the deviation from Ohm's law in this detector will have to be ex- 

 plained by the counter E.M.F. of polarisation in consequence of 

 electi-olysis^). The characteristic (curves in fig. 2) can l)e represented 



E e 



by the formula 7=: — j—, in which / is the current, £^ the applied 



E.M.F., and R a constant resistance, e the E.M.F. caused by pola- 

 risation. 



This E.M.F. of polarisation increases together with the applied 

 E.F.M. and will reach a maximum of about 3 Volts, as indicated 

 by curve b. As soon as the E.M.P\ of polarisation has leached this 

 maximum, the chaiacteristic will change into a straight line inter- 

 secting the horizontal axis at the point accurately represeining the 

 maximum value of the E.M.F. of polarisation. 



This maximum found with the aid of the characteiislic, may also 

 be obtained by dii-ect measuiement with the Wulf electrometer. 

 If this E.M.F. of polarisation did not occur, the characteristic would 

 be represented by the straight line c through the origin, parallel to 

 the straight pait of curve a. If the applied E.M.P\ is represented 

 by the line Ol\ liQ will represent the E.M.F. of polarisation which 

 can be deduced from the characteristic. The /^ may then be called the 



E E , 



"real resistance" of the detector and — = /^ the "apparent resi- 



1 E — e 



^) Armagnat. Journal de Physique, V, pag. 748, 1916. 



