1901.] Effect of Mercury Vapour on the Spectrum of Helium. 

 Description of Stations. 



25 



.Oinchirnian, 200 rnetn 



steamer workshops 

 Kawa (lat. 13° 55') 

 G-oz Abu Goma (lat. 13 ° 23 ') 

 Renk 



6 kilometres up stream of Jebel 



Ahmed Agha 

 16 „ 



Near Kaka (lat. 10° 30') 

 48 kilometres down stream of I 



Fashoda (lat. 10° 20') 

 8 kilometres up stream of moutli of 



Kirer Sobat, on Bahr el Abjad 

 Wood station on Bahr el Abyad, 



east of mouth of Bahr el Zaraf 



12 kilometres 

 Bahr el Zaraf, 20 kilometres from 



mouth 



Bahr el J ebel, 10 kilometres 



South of Hellet Nuer (lat. 8° 9' 30") 



Kenisa (lat. 6° 46' 0") 



Wood station, south of Bor on Bahr 



el Jebel (lat. 6° 5') 

 Wood station, south of Kiro on Bahr 



el Jebel (lat, 5° 15') 



Dip. 



Declination. Horizontal force. 



Declination. Dip. Horizontal force. 

 Right Dip. Horizontal force. 



" Note on the Effect of Mercury Vapour on the Spectrum of 

 Helium." By Professor J. Norman Collie, F.K.S. Keceived 

 June 3,— Bead June 19, 1902. 



Some years ago the author, in conjunction with Professor Kamsay, 

 published the results of some experiments relating to the visibility of the 

 spectrum of one gas in presence of another.* 



Since then some experiments have been made on the effect of 

 mercury vapour (when present in considerable quantity) on the 

 spectrum of helium in an ordinary Pliicker's tube, under the influence 

 of the electric discharge from an induction coil. When the spectrum 

 of helium is examined in an ordinary Pliicker's tube, it appears to be 

 a simple one consisting of only eight lines — two red, one yellow, three 

 green, one blue, and one violet. 



The spectrum, however, of the negative glow is much more com- 



* ' Rov. Soc. Proc.,' toI. 59, r . 2C2. 



