1920] Thermionic Valve in Wireless Telegraphy & Telephony 167 



capricious than the coherer, could be used to record the signals by 

 optical means, and also for a personal reason I wished to find one 

 which would appeal to the eye and not the ear only through the 

 telephone. Our electrical instruments for detecting feeble direct or 

 unidirectional currents are vastly more sensitive than any we have 

 for detecting alternating currents. Hence it seemed to me that we 

 should gain a great advantage if we could convert the feeble alternat- 

 ing currents in a wireless aerial into unidirectional currents which 

 could then affect a mirror galvanometer, or the more sensitive 

 Einthoven galvanometer. There were already in existence appliances 

 for effecting this conversion when the alternations or frequency was 

 low — namely, one hundred, or a few hundred per second. 



For example, if a plate of aluminium and one of carbon are 

 placed in a solution of sodic phosphate, this electrolytic cell permits 

 positive electricity to flow through it from the aluminium to the 

 carbon, but not in the opposite direction. The reason is because the 

 electrolysis covers the aluminium with an impervious film of hydroxide 

 in the first case and reduces this film in the second case. But such 

 electrolytic rectifiers, as they are called, are not effective for high 

 frequency currents, because the chemical actions on which the recti- 

 fication depends take time. After trying numerous devices my old 

 experiments on the Edison effect came to mind, and the question 

 arose whether a lamp with incandescent filament and metal collecting 

 plate would not provide what was required even for extra high 

 frequency currents, in virtue of the fact that the thermionic emission 

 would discharge the collecting plate instantly when positively elec- 

 trified, but not when negatively, xiccordingly I appealed to the 

 arbitrament of experiment, and the following arrangement was tried. 



Two coils of wire were placed at a distance, and in one of them 

 electric oscillations were created by the discharge of a Leyden jar. 

 The other coil had one terminal connected to the filament of a lamp, 

 and the collecting plate to one terminal of a galvanometer, the second 

 termiual of the latter being connected to the second terminal of 

 the coil. 



I found to my delight that my anticipations were correct, and 

 that electric oscillations created in the second coil by induction from 

 the first were rectified or converted into unidirectional gushes of 

 electricity which acted upon and deflected the galvanometer, as now 

 shown. 



I therefore named such a lamp with collecting metal plate used 

 for the above purpose, an oscillation valve, because it acts towards 

 electric currents as a valve in a water-pipe acts towards a current of 

 water. I soon found that for the purposes of wireless telegraphy 

 quite a small low voltage lamp with a metal cylinder placed round a 

 carbon or metal loop filament was a very effective rectifier, and could 

 be used for converting the feeble alternating currents in a wireless 

 receiving aerial into unidirectional currents capable of affecting a 



