1907.] on Recent Contributions to Electric Wave Telegraphy. 680 



condenser then begins to discharge back through it, and this increases 

 the current through the arc and therefore decreases the potential 

 difference of the carbons. The condenser therefore continues to 

 discharge. The action resembles that bv which the vibrations of the 

 column of air in an organ pipe controls the behaviour of the jet of 

 air from the mouth which impinges against its lip, forcing the jet of 

 air alternately into and outside the organ pipe, and so maintaining 

 stationary oscillations in it. The jet of air from the mouth of the 

 pipe corresponds to the continuous current arc, the closed or open 

 pipe associated with it is a resonant circuit and corresponds with the 

 condenser and inductance. 



Consider the state when the oscillations have been set up in the 

 condenser circuit. We must assume that there is a stream of electrons 

 from the negative terminal of the arc making their way across the 

 interspace to the positive terminal. If then we consider the state at 

 the instant when the condenser has reversed its charge, so that the 

 coating connected to the negative arc terminal is positively charged, 

 we see that there is a tendency for the stream of electrons to enter 

 the condenser and supply the deficiency represented by the positive 

 charge on that plate. They are, so to speak, sucked into the con- 

 denser. Accordingly this action either annuls or reduces the current 

 in the arc. When the condenser is charged to the potential difference 

 then existing between the terminals of the arc, no more electrons enter 

 it, and they then all travel across the arc. This increase in the arc 

 current is accompanied by a fall in the electronic density difference, 

 or the potential difference of the arc terminals, and the condenser 

 then begins to discharge across the arc, and still more reduces this 

 potential difference. Owing to the inductance in series with the con- 

 denser, or in other words in consequence of the kinetic energy of the 

 moving electrons, the condenser is not only discharged but charged 

 up again in the opposite direction.* It parts with the excess of 

 electrons forming the negative charge on its plate in connection with 

 the negative arc terminal, and that plate is left with a deficiency of 

 electrons, that is with a positive charge. Then the process repeats 

 itself over again. Two conditions seem necessary for the automatic 

 continuance of this process. First, the arc must be formed between 

 terminals of such nature and in such surroundings that rapid varia- 

 tions of current through it must cause correspondingly rapid and large 

 changes in the potential difference (P.D.) of the terminals in an inverse 

 sense, that is, as H. T. Simon has shown, there must be a steep falling 

 characteristic curve for the arc (see Fig. 10). f Secondly, the arc 



* The amplitude of the potential difference of the condenser terminals 

 may and does become very much greater than the mere steady potential 

 difference of the electrodes between which the arc is formed. Thus with a 

 P.D. of 220 or 300 volts across the arc the B-.M.S. of the condenser plates 

 may reach 1000 or 1500 volts. 



t A careful study of the phenomena of the electric arc between metal and 

 metal and carbon terminals in air and hydrogen has recently been made in 



YoL. XYIII. (No. lOlj 2 Y 



