168 



Mr 



. E. Gr. Bilham on 



a Compaq 



ison of the 









Arc. 















Mean 

 displace- 



Mean 

 displace- 











Wave-length 

 A. 



Class. 



Humphreys. 



Duffield. 



ment, 

 per Atm. 



ment, 

 per Atm. 













Low 

 Pressures. 



All 

 Pressures. 



10 Atm. 



20-100 

 Atm. 



in Arc. 



in Spark. 



1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



3722-63 



11. 





1-6 





2-2 



1-9 



2-9 



36-94 



II. 





1-2 





1-6 



1-4 



10 



39-38 



■II. 









1-2 



(1-2) 



1-0 



69-62 E 



IV. 



... 





4-b 



1-4 



(1-4) 



7-7 



75-71 



II. 





1-3 



10 



1-5 



1-4 



2-2 



83-67 



II. 





0-9 



1-3 



1-3 



11 



1-6 



3807-30 



II. 





11 



30 



1-5 



1-3 



1-8 



31-87 



II. 







3-2 



1-8 



d-8) 



36 



49 70 E 



IV. 













14-9 



58-40 



I. 





1-7 



3-9 



2-i 



1-9 



21 



3972-31 



III. 





1-1 



1-2 



0-8 



10 



2-8 



7370 



V. 





20 



4-4 



1-9 



2-0 



5-8 



4121-48 



III. 







3-9 



1-7 



(1-7) 



2-6 



42-47 



III. 





... 



10-5 







3-2 



4288 20 



V. 







16-2 



10 V 9 



(10-9) 



12-1 



4330-85 \ 

 31-78 J 

 59-76 



III. 





2-1 



6-3 



3-0 



2-6 



4-4 



V. 







11-5 



12-2 



(12-2) 



10-6 



4401-70 



V. 





4-8 



11-6 



120 



8-4 



10-2 



4459-25 



V. 





62 



10-2 



10-9 



8-6 



9-3 



62-65 



V. 







12-3 



9-5 



(9-5) 



9-9 



70-61 



V. 





8-5 



12-4 



110 



9-7 



8-9 



452020 







1-8 



31 



17 



1-8 





9269 



v. 





8-5 



14-1 



10-3 



9-4 



11-8 



4600-51 



IV. 





11-3 



13-8 



9-3 



10-3 





05-15 



V. 





7-8 



120 



9-5 



8-7 





48-82 



V. 





8-1 



140 



11-4 



9-8 





86-39 



III. 





8-0 



18-4 



11-7 



9-4 





4714-59 



V. 





6-7 



17-1 



111 



8-9 





56-70 



V. 





7-2 



15-7 



11-3 



9-3 





The mean shifts for the lines in each class have been com- 

 puted for comparison with the values found by Duffield for the 

 arc. Only lines figuring in both investigations have been 



included. m TT 



Table II. 



Class. 



Number 



of 

 Lines. 



Mean displacement per Atmosphere. 



Eatio 

 Spark : Arc. 



Arc (Duffield). 



Spark. 



I. 



II. 

 III. 

 IV. 



V. 



4 



24 



6 



1 



8 



1-95 



1-60 



1-57 



1-4 



9-84 



1-88 



1-85 



3-48 



7-7 



9-83 



0-96 

 1-16 

 2-22 

 5-50 

 1-00 



