
Bright Spectrum Lines. 499 
only the capillary of a tube where there is no liquid mercury 
present and thus producing no noticeable change in’ the 
pressure in the vacuum-tube, the kinetic energy of the atomic 
aggregations is increased such that many of the components 
of small intensity invisible before are now very readily seen. 
The number and intensity of the components were the same 
whether the tube was placed ‘“ side on” or “ end on,” that is 
whether the discharge was perpendicular or parallel to the 
propagation of the light through the slit. 
The introduction of capacity in parallel with the discharge 
circuit had an interesting effect. With three large leyden- 
jars, each gallon jars, the fringes were broadened and the 
finer components disappeared. ‘The effect appeared in every 
way analogous to that when the pressure was increased. 
The next step was to investigate the radiations from a 
mercury are and compare the results with those above. After 
many trials with different kinds of ares the following form 
(fig. +) was found the most satisfactory. The are is between 
Fig. 4. 

two mercury surfaces. A is an ordinary glass receiver of 
about 800 c.c. capacity. Over the mouth B is sealed a piece 
of plate-glass ; through the rubber stopper C is run a glass 
tube which is connected to the Geryk pump. Through the 
stopper D is placed an iron tube E of diameter 13 mms., along 
the axis of this is placeda porcelain tube F of diameter 8 mms. 
2M 2 
