Nipher — Nature of the Electric Discharge. 5 



ilar structure may sometimes exist within the negative 

 glow, is shown in Figs. A and B, Plate I. 



It appears probable that the oscillations which are set 

 up in the small gaps a and a' result in bringing about a 

 surging to and fro of the electric fluid within the metal 

 conductors leading to the spark-knobs. The oscillations 

 in a disruptive discharge are simultaneous in time, but 

 are distributed along the line of the discharge. They 

 are space alternations of dark and luminous columns, in 

 which the air is for the moment surging in opposite direc- 

 tions, as in an organ pipe sounding a high harmonic. 

 In the vacuum tube they are called striae. These space 

 alternations v/hich might be called sound waves may be 

 superposed on each of the successive time alternations 

 which may occur in a disruptive discharge. The success- 

 ive time alternations depend on resistance, self-induction 

 and capacity. The space alternations which are simul- 

 taneous in time, are electrically produced sound waves. 



It is now evident that the surging effects set up in the 

 lines leading to the main spark gap, account for the differ- 

 ence between the two discharges shown in Figs. B and C 

 of Plate XXV, in No. IV of Vol. XIX of these Transact- 

 ions. A small gap in the negative approach line at a 

 of Fig. 2, p. 64. (Fig. 1 of this paper) causes the discharge 

 from the negative terminal to become more widely diver- 

 gent. It is a dark discharge, and is not visible to the eye 

 or in the photograph. It surrounds the luminous drain- 

 age column, shown in Fig. B. 



When this gap at a is closed and a gap is made in the 

 positive line at a, these surging effects exist mainly in 

 the positive discharge line. To some extent they react 

 upon the entire system in each case. The discharge then 

 comes from zones of larger radius on the positive knob. 

 The positive streamers are then more widely divergent 

 in co-axial cones. The dark discharge then sweeps 

 through the region of the central axis of the cones which 

 diverge from the positive knob. This accounts for the 



