EFFECT OF I'KKSSURE UPON ARC SPECTRA.- SILVER. 39 



nebulous flutings do not occupy this particular part of the plate. At 200 atmosphere* 

 tlic spectrum is, as in other parts of the plate, nearly a continuous one. 



5. The broadening of the Lines. From the photographs we learn the following 

 facts within the region X 4000 to X 4600 : 



1 . All silver lines broaden under pressure. 



2. The broadening increases with the pressure, but different amounts of exposure 

 make it difficult to determine if the increase is continuous and linear with the 

 pressure. 



3. The broadening of the two 1st sub-series lines is, at normal atmospheric pressure, 

 unsymmetrical relatively to the superposed absorption line ; increase of pressure 

 increases the width of these lines, and their wings are then seen to consist of numbers 

 of fine lines which merge into one another at higher pressure. 



4. The broadening of the 2nd sub-series line (4476 '29) at normal atmospheric 

 pressure is unsymmetrical, being greater on the red side. Under pressure this is 

 more pronounced, but the line remains definite though its intensity diminishes. 



5. The broadening of the non-series line is distinctive because the line appears to 

 become the violet edge of a band which stretches further towards the red as the 

 pressure is increased, but at the highest pressure the violet edge has lost its character 

 as the head of a band. 



6. The distinction that was observed in the same region of the copper spectrum is 

 here also apparent : the 1st sub-series lines become hazy under pressure, resembling 

 hazy bands, and finally leaving only a cloudy banded appearance on the plate ; the 

 2nd sub-series lines remain definite lines without abnormal broadening, though they 

 ultimately disappear through a gradual weakening process. 



7. No relation has been found between the original intensity of a line and its width 

 under pressure. 



8. The magnitude of the broadening of the 1st sub-series lines is at 20 atmospheres 

 as great as 120 A.U. 



6. The Structural Character of the Wings of the Members of the 1st Sub- Series 

 under Pressure. The photographs of lines a and c at 5 and 20 atmospheres show 

 that the wings of those lines are of complex structure, being composed of a number of 

 closely packed lines which are comparatively fine at 5 atmospheres, and, though 

 broader at 20 atmospheres and somewhat merged into one another, are still recognisable 

 as the same lines. 



There is no obvious regularity in the shadings on the wings, which are dissimilar 

 for the two lines and also for the two wings of the same line. 



As the pressure increases, the wings of the lines extend outwards, and at 

 20 atmospheres some of the patches of light are separated from the original lines, 

 forming what is ultimately a band spectrum. 



On one photograph taken at each of the pressures 10 and 20 atmospheres the 



