24() Mr. G. Owen on the Discharge of 
At pressures of a few millimetres it was necessary to be 
very careful not to put a potential on the filament high 
enough to produce a luminous discharge. A delicate test for 
the presence or absence of a luminous discharge was afforded 
by the temperature of the filament. If a luminous discharge 
took place the temperature of the filament rose when the: 
potential was put on. The constancy of the temperature of 
the filament was, therefore, a guarantee that no luminous 
discharge occurred. 
Diagram 3. 
/600) 
75x 1C~9 ampere. 
Current 1 
The results tabulated above are represented diagrammatically 
in diagram 3. 
