230 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
In a]l cases where the condenser C was discharging itself gradually through the 
tube a low rustling sound was distinctly audible to sensitive ears so long as the 
stratification remained apparently perfectly steady. When the phase of confused 
stratification, which immediately precedes extinction, was reached, the sound in the 
Fig. 70. 
g p r' 
telephone became very loud and rose in pitch, with some tubes becoming quite shrill. 
These results, therefore, confirm the conclusion already arrived at from other experi- 
ments, namely, that the discharge in vacuum tubes is intermittent ; but we do not 
pretend that they make it manifest that stratification is dependent upon intermittence.* 
In the course of our experiments we have arrived at the following facts : — 
1. The discharge in a vacuum tube does not differ essentially from that in air and 
other gases at ordinary atmospheric pressures ; it cannot be considered as a 
current in the ordinary acceptation of the term, but must be of the nature of a 
disruptive discharge, the molecules of the gas acting as carriers of electrification. 
* Mr. Spottiswoode informs us (June 3, 1878) that he has also tried the telephone inserted in the 
circuit, both from the Holtz machine and from the great condenser, and found that the rushing noise 
was coincident with well developed striae. The sound, however, occasionally became inaudible (to human 
ears, D. and M.), and afterwards recovered its strength. When the tension in the condenser fell below 
a certain point, or the speed of the machine was reduced below a certain rate, indicated by a sudden 
change in the configuration of the striae, the rushing noise was replaced by a musical note, the pitch of which 
fell with the tension. The range of this note was in some cases considerably greater than an octave, and 
its pitch fell more often by semitones than gradually. The range both in pitch and in duration was 
increased by resistance introduced in the circuit. The pitch of the note was lowered by bringing the 
finger near to the tube, and thereby constricting the discharge. 
