420 Molecular Physics in High Vacua. [June, 
residual gas follows all the convolutions and designs into 
which skilful glass-blowers can manage to twist the glass. 
The negative pole being at one end and the positive pole 
at the other, the luminous phenomena seem to depend 
more on the positive than on the negative at an ordi- 
nary exhaustion such as has hitherto been used to get 
Fig. 5. 
the best phenomena of vacuum tubes. I have here two 
bulbs (Fig. 6), alike in shape and position of poles, the 
only difference being that one is at an exhaustion equal 
to a few millimetres of mercury, — such a moderate ex- 
haustion as will give stratifications or the ordinary luminous 
phenomena, — whilst the other is exhausted to about the 
millionth of an atmosphere. I will first connedt the mode- 
rately exhausted bulb with the indu( 5 tion-coil, and, retaining 
the pole at one side (a) always negative, I will put the posi- 
tive wire successively to the other three poles with which 
the bulb is furnished. You will see that as I change the 
position of the positive pole, the line of violet light 
joining the two poles changes. In this moderately ex- 
hausted bulb, therefore, the eledlric current always chooses 
the shortest path between the two poles, and moves about 
the bulb as I alter the position of the wires. 
