Certain Detectors used in Wireless Telegraphy. 535 



the power w delivered by the detector to the telephone and the 

 power W given in the form of electrical oscillations to the 

 detector, when the potential difference between the platinum 

 point and the large electrode has the value 2*9 volts — the 

 voltage of highest sensitiveness. Curve b shows the large 

 fall in sensitiveness caused by altering the applied electro- 

 motive force, the point still being anode. 



Jn the same way, curves c show the efficiency of the energy 

 transformation when the point is negative. Curve c is an 

 attempt to reach the best possible sensitiveness with the 

 point as cathode ; but it is to be remarked that when the 

 point is covered with hydrogen, the electrical conditions are 

 somewhat unstable, and the best potential difference is an 

 uncertain quantity. This is in strong contrast with the very 

 definite conditions that rule when the platinum point is 

 polarized with oxygen. This is clearly indicated by the 

 curves of fig. 3, where the ordinates represent the proportion 

 of energy delivered to the telephone when the applied voltage 

 has various values. 



This detector has received a very great deal of attention in 

 the past, but the precise mode of operation of the instrument 

 is still unknown. Reich*, after making experiments with 

 superposed direct current and alternating current of low 

 frequency, considered that the phenomena could only be 

 accounted for by a dissolution of the small electrode used as 

 anode and a simultaneous disappearance of oxygen — pro- 

 cesses purely chemical. Rothmund and Lessingf, using a 

 Blondlot oscillator and Lecher wires, and measuring the 

 potential difference across the detector and the current 

 through it when the oscillator was working and not working, 

 concluded that the whole action of the instrument depended 

 upon some unexplained " depolarization action " of the oscil- 

 lations ; and by using a variety of electrolytes, proved the 

 incorrectness of the hypothesis, which was a mere surmise 

 unsupported by scientific measurements, that the instrument 

 operated by resistance alterations due to the heat generated 

 in the liquid mass near the minute anode. Later Dieckmann J 

 measured the current changes that followed upon the passage 

 of strong oscillations of (unmeasured) intensity through a 

 detector. Later still, Austin §, using alternating current of 

 low frequency, showed that the detector was affected by 



* Phi/s. Zeitschr. v. p. 338 (1904). 



t Ann. d. P/u/s. xv. 1, p. 103 (1904). 



t Pkys. Zeitschr. v. p. 529 (1904). 



§ Bulletin, Bureau of Standards, i. 3. p. 435 (1905). 



