176 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



The so-called " thermoelectric receivers " of Austin," Pickard,'' and 

 Dunwoody.'' 



The " aiidion " of De Forest,*^ a very interesting and sensitive de- 

 vice, which though superficially resembling Professor Fleming's recti- 

 fier appears to act on an entirely different principle. 



The Cooper-Hewitt mercury receiver, about which little is known, 

 but which appears to be very sensitive. 



The following are some of the later methods of producing sustained 

 oscillations : 



The substitution of a number of arcs in series having terminals of 

 large heat capacity in place of the single arc in the arc method." 



The use of regulating or " fly-wheel " circuits in connection with 

 the arc method." 



The method of producing oscillations shown in plate 2, figure 1, by 

 using tw^o arcs and throwing the discharge from one side to the other 

 alternately at a frequency regulated by the constants of the electric 

 circuit." 



The condenser dynamo ^ which consists of two radially slotted 

 disks separated by a mica diaphragm, charged by a continuous cur- 

 rent source of potential, and rotating in opposite directions. 



Two-phase high-frequency dynamo method.^ 



Commutator method.'' In this method the high frequency is pro- 

 duced by means of a ball rotating at high speed on the interior sur- 

 face of a commutator (pi. 2, fig. 2). 



The helium arc method,* in which the arc is produced in helium 

 or argon or similar gases. 



The critical pressure method,^' in which the electrodes extend within 

 a certain critical distance, depending upon the pressure used, so that 

 the discharge always passes at the same voltage irrespective of the 

 distance between the electrodes. 



Methods of signaling. — Continuous production of waves but chang- 

 ing constants of sending circuit.'^ 



The inverted method of sending and the method of signaling by 

 sending dots, the interpretation of which is determined by similar 

 commutators at the sending and receiving stations. 



o Austin, United States application No. 319241, May 29, 1906. 

 2'Piclvarcl, United States application No. 342465, November 8, 1906. 

 c Dunwoody, United States patent No. 837616, March 23, 1906. 

 ^De Forest, United States patent No. 836070, January 18, 1906. 

 " United States application No. 291737, December 14, 1905. 

 ^ United States application No. 291739, December 14, 1905. 

 i? United States patent No. 793649, March 30, 1905. 

 " United States application No. 316521, May 12, 1906. 

 * United States application No. 351560, January 7, 1907. 

 i United States application No. 355787, February 4, 1907. 

 ^United States patents Nos. 706747, September 28, 1901; 706742, June 6, 

 1902 ; 727747, March 21, 1903. 



