696 



Professor J. A. Fleming 



[May 24. 



has come into use, commonly called the electrolytic receiver. In 

 one form it was invented in the United States by Fessenden, and 

 called by him a liquid barretter. It was independently discovered, 

 and described shortly afterwards in Germany by W. Schloemilch, and 

 is generally there called the electrolytic detector (see Fig. 12). It 

 consists of an electrolytic cell or vessel containing some electrolyte, 

 usually nitric acid. In it are placed two electrodes, one a metal or 

 carbon plate of large surface, and the other an extremely fine 

 platinum wire prepared by the AVollaston process, a very short length 

 of which is immersed in the liquid. A convenient plan is to prepare 

 a Wollaston wire of silver, having a core of platinum which is drawn 

 down until the latter is only 1/1 000th of a millimetre in diameter. 

 If the electrolyte is strong nitric acid, then when the above wire is 

 immersed to the depth of a millimetre the acid dissolves off the 



Fig. 12a. 

 Electrolytic Detector with Shunted Cell and Telephone. 



silver and leaves the fine platinum wire exposed as an electrode. 

 This cell has its two electrodes connected respectively to a receiving 

 antenna, and an earth plate, and also to a cii'cuit containing a shunted 

 voltaic cell and a telephone (see Fig. 12a). The voltaic cell sends a 

 current through the electrolyte in such a direction as to make the 

 fine wire the positive electrode or anode. Some dispute has taken 

 place whether the cell will work when the fine wire is the negative 

 electrode. Fessenden, who adopts a thermal theory of the cell, claims 

 with Rothmund and Lessing that it is equally sensitive, whether the 

 small electrode is positive or negative. 



According to one theory, the action of the cell as a wave detector 

 depends on the power of the oscillations to remove the so-called 

 polarisation of the electrodes or adhering films of ions. According to 

 another theory it is due to the heating action of the oscillations on 



