240 ANNALS NEW YORK ACADEMY OF SCIENCES 



grid condenser gives a leak which is independent of the value of the wing- 

 current and which effectually prevents trouble of this kind. With the 

 very high vacua now obtainable by the use of a molecular pump, there- 

 are practically no positive ions present, so that the auxiliary leak' is 

 always necessary. Under these conditions, it not only prevents paralysis 

 by the static, but it also removes from the grid condenser the excess of 

 negative electricity which accumulates in it, thereby increasing the sensi- 

 tiveness of the audion and the sharpness of the signals in the telephones. 

 The very high potentials to which the grid condenser may be charged by 

 the static are surprising. These potentials may be measured in a very 

 simple and accurate way, here described. After a stray has cut off the- 

 wing current, if we continuously increase the capacity of the grid con- 

 denser, the potential across it and hence the potential of the grid with 

 respect to the filament will be decreased inversely as the capacity. A 

 point will finally be reached where the grid potential is sufficiently re- 

 duced to allow the wing current to flow. When this occurs it indicates 

 that the potential of the grid condenser is slightly less than that shown 

 by the operating characteristic as necessary to reduce the wing current to- 

 zero. The potential to which the grid condenser was originally charged 

 is equal to this voltage times the ratio of the capacity of the condenser at 

 which the wing current began to flow to the original capacity. Voltages- 

 of over a hundred are not uncommonly reached by the grid and as one 

 volt represents a very strong signal, the difficulties of the static problem 

 are very forcibly presented. 



The fact that static of large amplitude produces almost invariably 

 a decrease in the wing current, while a signal (with beat reception) pro- 

 duces alternately an increase and decrease in the wing current, is a cir- 

 cumstance of which it should be possible to take advantage. The circuits 

 can be arranged to rectify the wing current in such, a way that only the 

 increases in this current are available to produce a response in the tele- 

 phones, but in carrying this method out, trouble is experienced from a 

 shifting zero. A better way of making use of the difference in response 

 is the following one. Suppose that we arrange two complete receiving 

 systems oscillating in step with each other, but so related to the antenna 

 that the beat currents in the two systems are 180 degrees apart. The 

 result of this will be that at the instant when the incoming signal is pro- 

 ducing an increase of current through the telephones in one receiver, it 

 will be producing a decrease of current through the telephones of the 

 other receiver; so that the two telephone currents are 180 degrees out of 

 phase. Static of large amplitude does not interact with the local fre- 

 quencies, and will produce simultaneously in each receiver a decrease in 



