170 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1908. 



receiver, in which a number of microscopic filaments are produced 

 between two terminals by electrolysis, which filaments are ruptured 

 by the wave-produced oscillations, thus increasing the resistance; 

 also the liquid coherer of Captain Ferrie, described by him as 

 follows : '^ 



The same effect of self-decohering coherence has been determined for a 

 contact of a metallic wire and a liquid conductor, acidulated water, contained 

 in a glass tube of small diameter, and placed under the same conditions as the 

 preceding. Always, the sensitiveness of this contact is very notably inferior 

 to that obtained in the experiments disclosed above. The maximum sensitive- 

 ness was obtained when the resistance of the imperfect contact was about 

 2,000 ohms and when the extremity of the metal wire scarcely grazed the 

 meniscus of the liquid. The results obtained were better with a copper wire, 

 attacked by the acidulated water, than with a platinum wire. 



This coherer probably acts through a chemical effect producing a 

 thin film of gas and has never come into use, doubtless because, as 

 Captain Ferrie points out, it is even less sensitive than the Marconi 

 coherer. Also the rectifier of Pupin,^ in which the terminals are 

 placed so closely together that practically no energy is absorbed in the 

 receiver, in order that the rectified energy may be utilized outside in 

 the external circuit, in opposition to the liquid barretter, where the 

 position of the terminals is such that all the received wave energy is 

 absorbed in the barretter for the purpose of producing a secondary 

 effect, and so influencing the current in a shunted local circuit. 



METHODS or OBTAINING SUSTAINED OSCILLATIONS. 



Spa7'h-gap\, and local oscillatory or " tank " circuit. — Prof. Elihu 

 Thomson discovered that by using a transformer w^ithout an iron 

 core (the well-known Elihu Thomson air-core transformer, later used 

 by Tesla and others) and a spark-gap and condenser in the primary 

 circuit, and with the secondary circuit suitably tuned great resonant 

 rises of potential could be obtained. In 1892 he constructed such a 

 transformer giving discharges 64 inches long.'" 



The same method was later used by Tesla ^ in his experimental 

 researches and in his attempt to carry out Loomis's " method of trans- 

 mitting a current through a hypothetical conducting stratum in the 

 upper regions of the atmosphere. 



The device, suitably modified for wireless telegraphic purposes, so 

 as to give, instead of a continuously cumulative rise of potential, an 

 initial rise of potential followed by a gradual feeding in of the 

 energy from the local circuit to supply the energy lost from radiation, 



" Blondel, L'Eclairage Electrique, September 29, 1900. 

 6 Pupin, United States patent No. 713044, January 4, 1898. 

 « Electrical World, February 20 and 27, 1892. 

 ^ United States patent No. 645516, September 2, 1897. 

 e Loomis, United States patent No. 129971, July 30, 1872. 



