ix.] CONTORTIONS OF F. 119 



strange behaviour of the F line. Its coincidence with the 

 corresponding dark line could not always be satisfactorily made 

 out it appeared to be more refrangible. Again, a few days 

 later, when observed with a tangential slit, the line assumed the 

 appearance shown in Fig. 52. 



In the spectrum of the light proceeding from the exact limb 

 of the sun the bright line was seen more refrangible than F, 

 but in the spectrum of the prominence at some distance above 

 the sun the black line F was eclipsed. Hence it appeared that 

 away from the sun's surface the substance which produced the 



FIG. 52. Non-coincidence of bright and dark F line when tangential slit is used, 

 and when both photospheric and chromospheric light is admitted. 



line gave out light of less refrangibility than it did at the 

 surface. 



Again, the bright line was sometimes strangely contorted, as 

 shown in Fig. 53, sometimes being violently deflected to the 

 right or left and sometimes broken as in Fig. 54, part of it 

 being torn away considerably to the more refrangible part of 

 the spectrum. We have in the first figure the F line. The 

 slit the perfectly straight slit has been worked round the 

 limb in search of a prominence, and it has found one. But 



