700 Professor J. A. Fleming [May 24, 



employed a telephone in a distant closed secondary circuit to detect the 

 masfnetic field so produced, signals being made by interrupting the 

 primary current. I have, however, found a means of greatly 

 improving this form of wireless telegraphy. In a closed primary 

 circuit I establish continuous undamped oscillations of, say a quarter 

 of a million frequency by the arc method. At a distance I place a 

 syntonic secondary circuit containing my oscillation valve as a 

 detector, a telephone being used with it connected between the 

 middle plate and negative filament terminal. Both the primary 

 circuit and secondary circuit are connected to earth at some point. 

 The signals are made by breaking and making the earth connection 

 of the transmitter in accordance with Morse code. When the 

 earth connection is made at both ends a sound is heard in the tele- 

 phone, but not when it is broken. This seems to depend upon the 

 fact that the oscillations produced by the arc method are not abso- 

 lutely continuous, but cut up into groups, as already proved by the 

 experiment with the rapidly-moving neon tube and helix. 



I have found that it is not necessary to employ a high voltage 

 carbon filament, a small lamp with 4-volt filament, taking about one 

 ampere, works quite as w^ell as a wireless telegraph receiver as a 12 or 

 100 volt lamp. The filament has, however, to be at a certain critical 

 temperature to obtain the best result ; the vacuum also has to be 

 extremely good. There are, no doubt, many possible variations of 

 the above-mentioned type of oscillation valve wave detector. Every 

 glass vessel containing rarefied gases or mercury vapour having 

 electrodes of different sizes or shapes or temperatures, has some 

 degree of unilateral conductivity, and can be used in the above 

 manner to separate out the two constituent currents of an electrical 

 oscillation, and make them detectable by an ordinary galvanometer 

 or telephone. I have also tried with some success a flame in which 

 two platinum wires are immersed, one of which carries a bead of 

 potassium sulphate as a means of rectifying oscillations of high 

 frequency. It is well known that negative ions are then liberated 

 in the flame, and negative electricity can pass over more freely from 

 the electrode which cames the bead of salt to the other than in the 

 opposite direction. I have not, however, found anything as simple 

 and useful as the above-described low-voltage carbon filament glow 

 lamp. Moreover, other inventors have endorsed its utility by 

 granting it the compliment of imitation. In October 1906, Dr. de 

 Forest described to the American Institute of Electrical Engineers 

 an appliance he called an " audion," which is merely a replica of my 

 oscillation valve, described to the Royal Society eighteen months 

 previously and to the Physical Society of London six months before, 

 particularly with reference to its use as a wireless telegraph receiver. 

 Apart from the name the only difl'erence introduced by him was to 

 substitute a telephone and battery in series connected between the 

 middle plate and positive terminal of the filament, for the 



