from Long Vacuum Tubes. 



733 



heavy current and put a lamp bank in series with the pri- 

 mary of the transformer ; we shall now find a very curious 

 relation between the spectroscopic phenomena and the 

 strength of the current. 



Starting with only one lamp in the circuit, the direct- 

 vision prism shows that the secondary spectrum alone appears 

 in the entire tube, with perhaps a trace of H a and H^ in the 

 central part. 



On gradually adding lamps we find that the Balmer series 

 brightens tremendously with each increment of current. 



The secondary spectrum in the central part of the tube, 

 though it may brighten a little with the first small incre- 

 ments of current, presently begins to weaken with each 

 additional lamp, eventually reaching a minimum intensity 

 for a certain current value in the primary of the transformer 

 (3 amps, in the present case). Further increase of the 

 current brightens the secondary, though the intensity of 

 the Balmer lines is now so great that the secondary can be 

 seen only by employing the green screen. 



The relations between the intensities of the secondary and 

 Balmer series spectra and the current strength are roughly 

 indicated in fig. 2. The general character of the secondary 



Tin-. 2. 









A 



j 



>^~ 





^-^' 



i 



Amperes in Transformer Pr/ma/y 



spectrum in the visible regions does not vary much with the 

 current strength or conditions of the tube. 



Between the 4th hydrogen line and the head oi the series 

 there is a very marked change in the secondary spectrum as 

 the current increases. 



As I staied in the earlier paper, the limit to the number ot' 

 lines of the Balmer series which can be photographed depends 

 upon the extent to which the 2nd spectrum and the continuous 



