HERTZIAN \YAVE WIRELESS TELEGRAPHY. 557 



chains of metallic particles and thus interrupt the current i)assing 

 through the telephone quite suddenly, which is heard as a slight tick 

 by an ear applied to it. As soon as the wave ceases, the chain of metallic 

 particles is reestablished, so that the appliance is always in a condition 

 to be affected by a wave. It is said that this breaking up and reforma- 

 tion of the chains of metallic particles is so rapid that a short spark 

 made at the transmitting station is heard as a tick in the telephone, 

 l)ut a rapid succession of oscillatory sparks is heard as a short con- 

 tinuous sound; hence the two signals necessary for alphabetical con- 

 versation can be transmitted. 



Another receiver which has some resemblance to the above, although 

 different in principle, is that of jSTeugschwender.* In this arrange- 

 ment, which to a certain extent resembles the Schiifer detector, a glass 

 ])late has upon it a deposit of silver in the form of a strip, which is cut 

 across at one place, thus interrupting it. If the cut is breathed upon 

 or placed in a moist atmosphere, a little dew is deposited upon the 

 glass, which bridges over the cut in the metal and creates an electric 

 continuity. Hence a small current can be passed across the gap and 

 through a telephone by one or two cells of a battery. If, however, an 

 electric oscillation passes across the gap on its way from an aerial to 

 the earth, then the continuity of the liquid film is destroyed and the 

 current is interrupted and a sound created in the telephone. 



The opinion has been expressed by Sir Oliver Lodge that in this 

 case the interruption of the circuit which occurs is really due to the 

 coalescence of minute water particles into larger drops, as when vapor 

 is condensed into rain, and hence the continuity of the material is 

 interrupted. 



We must then make a brief reference to other kimiascopes which 

 depend upon the heating power of an electrical oscillation, which it 

 possesses in common with every other form of electric current. Pro- 

 fessor E. A. Fessendenf has constructed a very ingenious thermal 

 receiver in the following manner: An extremely fine platinum w^ire, 

 about 0.003 of an inch in diameter, is embedded in the middle of a 

 silver wire about one tenth of an inch in diameter, like the wick of a 

 candle. This compound wire is then drawn down until the diameter 

 of the silver wire is only .002 of an inch, and hence the platinum 

 wire in its interior being reduced in the same ratio, will have been 

 drawn to a diameter of 0.00006 of an inch. A short piece of this drawn 

 wire is then bent into a loop and the ends fixed to wires. The tip of 

 the loop is then immersed in nitric acid and dissolved in the silver, 

 leaving an exquisitely fine platinum wire a few hundreds of an inch in 



* See The Electrical Revieic, Vol. XLIV., 1899, May 26; Wied Ann., Vol. 

 LXVIII., p. 92; or German Patent Specification, No. 107,843. 

 t U. S. A. Patent Specification, No. 706,742, 1902. 



