242 ANNALS NEW YORK ACADEMY OF SCIENCES 



receiver and 180 degrees out of phase with the local oscillations of the 

 other. This produces the desired result in the currents through the 

 transformers of the circuit T, which act in the manner already described. 



It is found in practice that the oscillations set up in each system by 

 the incoming signals tend to neutralize each other through the circuit 

 L^G-JJ^L-^. This effect is avoided by introducing in the wing circuits 

 a difEerential coupling arranged to neutralize the coupling between the 

 two grid circuits. It is possible to do this, as it does not affect the coup- 

 ling of either receiver with the antenna, and does not interfere with the 

 local operation until the effective coupling between the two systems is 

 reduced to a point below which they will no longer remain in step. There 

 are other ways of securing the same result, but the system shown will 

 illustrate the general procedure in carrying out this method of balancing. 



The practical results obtainable with these receivers may perhaps be 

 of interest. At the present time, signals from all high-power stations 

 from Eilvese (Germany) to Honolulu are heard day and night at Colum- 

 bia University with a single audion receiver. Cascade systems give cor- 

 respondingly better results, two stages being sufficient to make the night 

 signals of Honolulu audible throughout the operating room. Inter- 

 ference with the signals from Nauen by the arc station at Kewcastle, 

 New Brimswick (Canada), is very easily eliminated by means of an 

 audio frequency tuning circuit; and this is the most severe interference 

 we have yet experienced, the two frequencies sometimes differing by less 

 than 1 per cent and the arc signals being much the stronger. 



These receivers have been developed in the Hartley Eesearch Labo- 

 ratory, Columbia University, and are mainly the result of a proper un- 

 derstanding and interpretation of the key to the action of the audion — 

 the grid potential-wing current curve. In conclusion, I want to point 

 out that none of the methods of producing amplification or oscillation 

 depend on a critical gas action; they depend solely on the relay action of 

 the tube employed (electron or gas relay) and the proper arrangement 

 •of its controlling circuits. 



SUMMARY 



The action of the audion as a detector and simple amplifier is ex- 

 plained, with the method of verification of the theory by means of oscil- 

 lograms. To reenforce the oscillations in the grid circuit two methods 

 are employed. First, to couple the grid circuit to the wing circuit and 

 arrange the latter to permit radio frequency currents to pass freely in 



