Induced Alternating Cic? , re?it Discharge. 69 



discharge for an hour and a half to secure the lines, but, as no 

 lines were obtained, and none of the ultra-violet lines of the 

 solar spectrum were visible, it was suspected that the staining 

 with cyanine, while it made the plate more sensitive to the red 

 rays, diminished the sensibility to the ultra-violet, and there- 

 fore, that probably the lines sought were in the ultra-violet. 



Plates stained with erythrosine were next tried. It was 

 found that an exposure of five minutes gave the ultra-violet 

 spectrum of the sun's rays together with the lines in the red, 

 in the neighborhood of the lines sought for. To obtain the 

 lines several exposures to the discharge of an hour and a half 

 were made and a few feeble lines obtained. The time of 

 exposure was then increased to two 'hours. Upon develop- 

 ment the lines upon the first plate tried were sharp and dis- 

 tinct. The wave lengths were calculated as accurately as possi- 

 ble by means of the comparison solar spectrum and Rowland's 

 charts. This is first done on the supposition that they are in 

 the lower part of the first spectrum and the result divided by 

 two to get their true wave length in the ultra-violet of the 

 second spectrum, since it was now regarded as almost certain 

 that they were ultra-violet lines owing to the fact that we did 

 not obtain them with plates stained with cyanine, which makes 

 them more sensitive to the red rays, and on the contrary did 

 obtain them when the plates were stained with erythrosine, 

 which increases their sensitiveness to the ultra-violet, as was 

 proven by exposing a dry unstained plate to the sun's rays 

 when, although the ultra-violet lines were visible, they were 

 exceedingly faint. 



The wavelengths as calculated by means of Rowland's charts of 

 the solar spectrum and the comparison on the plate are as follows : 



3063-66 



3086-48 



3105-71 



3063-83 



3087-40 



3106-02 



3064-30 



3089-80 



3106-55 



3065-04 



3089-94 



3109-46 



3065-17 



3090-24 



3110-30 



3066-27 



3091-35 



3112-17 



3068-00 



3091-48 



311343 



3068-31 



3092-45 



3114-85 



3069-11 



3092-84 



3115-49 



3070-02 







3070-52 



3094-70 



3117-87 



3070-83 



3095-41 



3118-03 



3072*05 



3096-16 



3122-70 



3078-47 



3096*87 



312414 



3080-06 



3098-63 



3130-46 



3080-27 



309953 



3134-55 



3081-65 



3101-20 





3083-35 



3102-13 





3085-25 



3102-35 





