698 



Professor J. A. Flemmg 



[May 24, 



exhibits this power in a marked degree. Negative electricity escapes 

 freely froDi it, but not positive. In 1004 I was endeavouring to find 

 some way of rectifying electrical oscillations, that is, of separating out 

 the two sets of alternate currents and making them separately detect- 

 able by an ordinary galvanometer. It occurred to me to make use of a 

 carbon filament lamp, having a metal cylinder insulated in the bulb 

 surrounding the filament, the cylinder being connected to a platinum 

 wire sealed through the bulb (see Fig. 1;^)). This lamp was then used 

 as follows. A circuit was connected between the terminal of the metal 

 plate and the negative terminal of the filament, the latter Ijeing made 

 brightly incandescent by a small battery. In this circuit a galva- 

 nometer and one circuit of a small transformer or induction coil 



Fig. 14. — Oscillation Valve or Glow Lamp Detector, used as a 

 Receiver in Electric Wave Telegraphy. 



was inserted. On connecting the other circuit of the transformer 

 between an antenna and the earth, I found that oscillations set up in 

 the antenna caused a deflection in the ordinary mirror-galvanometer 

 (see Fig. 14). The action is as follows. The antenna oscillations 

 induce others in the circuit of the transformer, which is in connection 

 with th(! lamp. A movement of electricity in this circuit, which con- 

 sists in the flow of negative electricity from the filament to the plate 

 through the vacuum, can take place, since this negative electricity is, 

 so to speak, carried across the vacuous space by the electrons emitted 

 from the hot carbon. On the other hand, negative electricity cannot 

 flow in the opposite direction. Hence the glow-lamp separates out the 

 two oppositely directed movements of electricity and allows only one 

 to pass. I therefore called the appliance an oscillation valve. This 



