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glass walls, the front surface of the cathode is coated with beryllium. 

 This metal resists the disintegrating action of the glow discharge very 

 satisfactorily and gives the lamp a prolonged life. Other metal sur- 

 faces in the tube are shielded from the discharge by mica plates; and 



* 





Fig. 13 — Water-cooled neon lamp. 



the discharge passes from the frame-like anode to the front surface of 

 the cathode, covering it with a brilliant layer of uniform cathode glow. 

 Pure neon in a plate type of lamp gives a very inferior reproduction 

 of an image. The impedance of the lamp is relatively high and com- 

 prises both a resistance and a reactance which vary with frequency. 

 The variation in the impedance causes a relative loss in the frequency 

 components of the signal and also introduces spurious phase shifts. 



