NICKEL UNDER MODERATE PRESSURES. 
371 
8. The shifts are larger for unreversed than for reversed lines and are greatest for 
lines broadening unsymmetrically towards the red. 
9. Certain abnormalities in the behaviour under pressure indicate the existence of 
enhanced lines, having wave-lengths 3514'14 and 3608'98 (approximately) almost 
coincident with two nickel arc lines. 
In conclusion I wish to express my gratitude to Prof. A. Fowler for his helpful 
interest in this research, and also to Mr. Colebrook, under whose supervision almost 
the whole of the apparatus was constructed in the workshops of the Imperial College. 
Description of Plates. 
Plate 6. 
Changes in character of lines in the spark spectrum of nickel under pressure- 
A. Pressure, 1 atmosphere. 
B. ,, 6 atmospheres. 
C. „ 11 
Plate 7. 
Apparent violet displacement of X3514— 
(l) Spark and arc comparison. 
A. Spark. 
B. Arc. 
(2) Spark under pressure. 
A-. Normal spark. 
C. Pressure, 11 atmospheres. 
Abnormal shift of X 3609. 
(3) Spark and arc comparison. 
A. Spark. 
B. Arc. 
(Scale of reproduction :—1 mm. = 0'43 A.U.) 
(4) Spark under pressure. 
A. Normal spark. 
C. Pressure, 11 atmospheres. 
3 b 2 
