168 



Professor J. A. Fleming 



[May 21, 



telephone or galvanometer. It was almost immediately adopted in 

 practical wireless telegraphy as a simple and easily managed detector, 

 and the intermittent rectified currents were passed through a tele- 

 phone (Fig. 3).* 



It may be just as well to mention here that there are two systems 

 of wave generation in use in wireless telegraphy. In one the waves 

 are created by powerful intermittent condenser discharges. These 



Pig. 3. — Fleming Oscillation Valve, on Stand. 



C, metal cylinder surrounding the filament of a glow lamp, 

 and connected to a terminal T 3 . B, glass bulb highly exhausted. 

 T, T 2 , terminals of the lamp filament. 



waves are radiated in groups of about twenty to fifty waves, and 300 

 to 500 such groups are sent out per second. The receiving aerial 



* For the purposes of patent litigation and controversy it has frequently been 

 urged that there was little or no invention involved in thus applying an incan- 

 descent lamp with a metal cylinder in the bulb as a detector for wireless 

 waves, seeing that such an appliance had already been made by Mr. Edison. 

 Important legal judgments confirmed by the United States Court of Appeals 

 have, however, held that it did constitute invention, and of a very meritorious 

 device : and that, prior to the disclosure by me, it was not known to men 

 skilled in the radio art that such a device would rectify and detect oscillations 

 of high frequency as used in wireless telegraphy. The invention therefore 

 consists not in the appliance in itself, but in the altogether new, unexpected, 

 and highly useful application made of it by me in radiotelegraph} 7 , which 

 opened a vast field for subsequent invention based on the same facts of 

 thermionic emission. 



