vin.] SPECTRUM OF FACULA. 105 



once a compliance with this anticipation in the lines of hydrogen, 

 magnesium, and sodium. The line 768'1 is not less strikingly in 

 concordance, if it be regarded as 768'?* (the ? indicates doubt as to 

 the tenths of the scale, and * absence of a corresponding black 

 line) of Young's catalogue of chromospheric lines. The lines 1828'6 

 and 1830'9, with others of the same class, probably have their 

 origin in the medium which exerts the general absorption, and thus 

 are allied to our telluric lines. It also seems probable that the 

 chromosphere is too transparent to reverse many of its lines. That 

 this is the case in the helium lines is tolerably certain." 



5. Spectrum of the Faculce. 



When a facula is brought on to the slit of the spectroscope, it 

 manifests its presence by a band of greater brightness than 

 elsewhere running . along the whole length of the spectrum. 

 We have in fact an indication of less absorption, general as 

 evidenced by the greater brightness of the continuous spectrum, 

 and selective as shown by the thinning and even disappearance 

 of some of the dark lines. 



This and other observations have led to the conclusion that the 

 faculse are elevated above the general surface as the spots are 

 depressed, that they are in fact the higher cloud-domes of the 

 photosphere. This will at once explain why the faculse are best 

 seen near the sun's limb. The difference between the general 

 absorption of a facula and that of the general surface of the sun 

 is so small, that it may be scarcely perceptible on the centre of 

 the disc, but becomes very apparent at the limb, where a greater 

 thickness of atmosphere is brought into play. 



It is seen then that the new method actually does give us 

 important spectroscopic differences, not only between the spectra 

 of spots and faculse, but between the spectra of both spots and 

 faculse as contrasted with that of the general surface. 



