1874.] Mr. J. N. Lockyer's Spectroscopic Notes. No. IV. 379 



Fig. 3. 



4. Figs. 4 and 5 give two variations sometimes observed fig. 4 showing 

 the darkening in the absorption and an increased steepness in the curve ; 

 tig. 5 the simultaneous existence of apparently different absorptions, 

 all bounded by D on one side, but by different curves on the other, and 

 being of different intensities. 



Fig. 4. 



Fig. 5. 



5. Although, in the preceding drawings, I have represented this uni- 

 lateral widening exclusively on the more refrangible side of D, I have 

 observed it on the other, though scarcely so frequently. 



6. Accompanying these appearances, but generally best visible when 

 the absorption with curved boundary is visible on both sides of D, is a 

 brilliant boundary replacing the mere change of shade. 



7. At times the brilliant boundary is continuous across D, as shown in 

 fig. 6 ; but I append figs. 7 and 8 to show that the phenomena on either 

 side of D are independent of each other. 



6. 



