along positive ray parabolas of atoms and molecules of hydrogen 321 



shape of cathode {I.e., p. 20) may be said in a sense to combine 

 both forms and was designed to give long and bright parabolas 

 at the same time allowing the discharge to pass easily at very low 

 pressures. The present results however lead one to recommend a 

 concave cathode similar to those used in X-ray focus tubes but 

 pushed further forward into the neck of the bulb, for though this 

 form requires a rather higher pressure this objection is more than 

 counterbalanced by the great increase in efficiency. Plane cathodes, 

 as was expected, give effects midway between the other forms. 



O 



/ 



Fig. 3. General Type. 



Under very exact conditions of pressure, etc. it is possible to 

 obtain the pure atomic type with plane cathodes but no conditions 

 have yet been found under which convex ones will give it. 



These results seem to indicate that atomic ions are formed by 

 the passage of the stream of cathode rays through the Crookes 

 dark space molecular ones tending rather to be formed in the 

 negative glow. The axial intensity of the cathode stream is 

 enormously increased by the concavity of the cathode while that 

 of the negative glow does not appear to be affected to anything 

 like the same extent. 



22 2 



