EFFECT OF PRESSURE UPON ARC SPECTRA. 
143 
Tables III. and IV., Diagrams V. and VI. 
The mean values of the displacements have been found for each group at each 
pressure, and the results for Set A are given in Table III., and those for Set B in 
Table IV. 
For Groups I. and III. the reversed have been separated from the unreversed lines. 
/Pressures /n Atmospheres 
Diagram Y. 
Diagrams V. and VI. have been plotted from the Tables III. and IV. respectively, 
and refer both to reversed and unreversed lines. They emphasize the difference in 
magnitude of the displacements of the three groups, and exhibit graphically their 
rates of increase with pressure. 
The increase of wave-length corresponding to a difference in pressure of 1 atmo¬ 
sphere, calculated on the assumption of a linear relation, is given below :— 
