Effect of Pressure upon Arc Spectra. 



575 



of a continuous spectrum appear. A few lines form an 

 exception to this general rule, and are more intense at the 

 hioher than at the lower pressure. 



The accompanying table gives a list of all lines clearly 

 visible on the photographs of the spectra taken at 17 and 

 105 mm. pressure (see Plate XXV. a and e) . The relative 

 intensities are given in colunms 2 and 3 for these two 

 pressures, and to more clearly emphasize the selective effect, 

 the intensities of these same lines in the self-induction spark 

 and ordinary arc are included in columns 4 and 5. The wave- 

 lengths and intensities of the arc are taken from Kayser and 

 Runge ; the intensities of the self-induction spark from 

 Hemsalech. 



Table of Iron Glow Spectra. 





Pressure in mm. Hg. 



Volts at Alternator 

 Terminals. 



Amperes. 



a ... 

 b ... 

 c ... 



d ... 



e ... 



17 

 S3 

 46- 



78 



105 



Self-induction spark at 

 atmospheric pressure. 



550 

 450 

 570 

 600 

 640 



6 



7 

 8 

 8 

 8 



Iron Glow Spectrum. 





1 

 Intensities*. | 





Intensities * . 



Wave-lengths. 





I 

 K&E. 



Wave-lengths. 









e. 



a. 



H. 



e. 



a. 



H. 



K&K. 



5455-80 



4 



In 



8s 



10 



5171-71 1 

 5167-50 J 



3n 



In 



2s 



8 



5447-05 



4 



In 



8s 



10 



10 



5434-66 



5 



In 



4s 



8 



5105-66 



1 



1 





8 



5405-91 



4 



In 



58 



10 



4957-80 1 

 4957-43 / 





4 



12 



8 



5397-27 



4 



In 



5s 



10 



i 



6 



5371-62 



4 



In 



4s 



10 



4920-63 1 

 4919-11 \ 





4 



6s 



10 



5328 15 1 

 5324-31 ] 



6n 



3n 



8s 



10 





5 s 



8 



4s 



10 



4891-62 1 





3 



7s 



10 



5269-65 



7 



4 



10 



10 n 



4890 89 J 





6s 



8 



523305 



1 



On 



s 



10 



4872-25 

 4871-43/ 







3 s 



8 

















OS 



^ 



In tlie accompanying table n=: nebulous, rf = jharp. 



