84 
MESSRS. W. DE LA RUE AND H. W. MULLER OR THE 
The electric arc. 
We have already stated ” that “ 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!' . . . 
We had a strong conviction while writing the above that the stratified discharge in a 
vacuum tube was simply a magnified form of arc, and in consequence we planned out 
a series of experiments to test the correctness of this supposition ; these were com- 
Fig. 79. 
menced in October, 1878, and although not yet concluded, we venture to lay before 
the Society an account of the results hitherto obtained, as they seem to support the 
view that the arc and the stratified discharge are merely modifications of the same 
phenomenon. 
The experiments were made in a bell-jar, containing the terminals, which could be 
gradually exhausted after having been filled with air or other gas. One of the terminals 
* Part II., page 230, 
