500 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
Fig. 22. 
Electrical condition of a, gas in a vacuum tube in the vicinity of the negative terminal. 
The preceding experiments, in relation to potential at different parts of a column of 
gas, suggested the desirability of probing the electrical condition of a tube in the 
vicinity of the terminals, more especially the negative. Professor Stokes suggested 
that this might be conveniently done by means of wires fixed at different distances 
from it, provided the wires were covered with miniature glass tubes reaching nearly 
to their extremities. Accordingly a bulb was prepared of the form and construction 
represented half-size in fig. 23, in which P is a terminal in the shape of a point, to 
serve as the positive, N, another in the shape of a ring, to serve as the negative, both 
Fig. 23. 
