ELECTRIC WAVE TELEGRAPH Y—FLEMING. 181 
in the United States by Fessenden, and called by him a liquid barret- 
ter. It was independently discovered, and described shortly after- 
wards 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 Wol- 
laston 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 one 
one-thousandth of a millimeter in diameter. If the electrolyte is 
strong nitric acid, then when the above wire is immersed to the depth 
of a millimeter the acid dissolves off the silver and leaves the fine 
platinum wire exposed as an electrode. This cell has its two elec- 
trodes connected respectively to a receiving antenna, and an earth 
plate, and also to a circuit containing a shunted voltaic cell and a tele- 
phone. (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. 4, 
Some dispute has taken place 
whether the cell will work 
when the fine wire is the nega- c Ki 
tive electrode. Fessenden, who WOVUUULD B 
adopts a thermal theory of the R 
cell, claims with Rothmund and 
Lessing that it is equally sen- SS 
sitive, whether the small elec- z z 
trode is positive or negative. WM 
According to one theory, the | | 
action of the cell as a wave de- 
tector depends on the power of Fie 12A.—Hlectrolytic detector with shunted 
3 t cell and telephone. 
the oscillations to remove the 
so-called polarization of the electrodes or adhering films of ions. Ac- 
cording to another theory it is due to the heating action of the oscilla- 
tions on the small electrode and liquid in its neighborhood. In any 
case, the action is just as if the resistance of the electrolytic cell were 
suddenly changed, either increased or decreased. It has also been 
found by Rothmund and Lessing that the cell may be made to supply 
its own electromotive force. If we form a simple polarizable voltaic 
cell with fine zine and platinum wires immersed in dilute acid and con- 
nect a telephone or high resistance galvanometer to these elements; 
then, when electric oscillations pass through the cell, the current sent 
by it through the telephone or galvanometer is momentarily increased. 
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