On the Enhanced Lines in the Spectrum of the Chromosphere. 179 



not appear as bright on the eclipse plates ; one pair is doubtful, 

 the remainder occur as quite strong lines of the ordinary dark line 

 spectrum, and hence would be expected to appear in the reversing 

 layer, as they do." 



If a difference of 0"3 tenth metre be allowed between the wave- 

 length of an eclipse line and that of the possibly corresponding metallic 

 line (and in some cases Professor Frost accepts a difference of 0*35 or 

 more between his adopted wave-length and Rowland's solar wave- 

 length), the seventeen lines above mentioned dwindle down to ten. 

 That leaves, then, thirty-eight out of forty-eight of the enhanced lines, 

 or about 80 per cent., which agree in position within 0'3 tenth-metre 

 with the eclipse lines. Surely this shows as close a relationship between 

 the enhanced lines of titanium and the eclipse lines, as that between the 

 latter and the stronger of the Fraunhofer lines, for it is stated on 

 p. 345, "of 171 of Rowland's lines, 61 per cent, were measured as 

 bright on the plates." 



Nowhere has it been contended that the whole set of enhanced lines 

 belonging to any one metal are represented in the spectrum of any one 

 celestial body ; what has been stated is that the enhanced lines of some 

 of the metals are, in general, of paramount importance in the spectra 

 of some stars (e.g., a Cygni), specially prominent in others (e.g., y Cygni, 

 the spectrum of which, with the exception of the absence of helium 

 lines, very closely resembles that of the chromosphere), and are a 

 marked feature of the spectrum of the chromosphere itself. 



Professor Frost either has not noticed, or does not point out, that 

 most of the enhanced lines of titanium, as compared with the ordinary 

 lines of that element, are specially prominent, and are amongst the 

 lines of greatest intensity in his list, as shown in the following table. 

 The first two columns of the table contain respectively the wave- 

 lengths and intensities of Rowland's solar lines (in the region covered 

 by the eclipse lines), which have an intensity of 2 or more, and which 

 have been ascribed to Ti only. Double assignations, of which Ti forms 

 one, have been omitted, as it is difficult, if not impossible, to determine 

 what proportion of the intensity of the solar line is due to each element. 

 The third column indicates whether the titanium line at the given 

 wave-length is an enhanced one or not. The fourth gives the wave- 

 lengths, the fifth and sixth the intensities, and the eighth the origins 

 which Professor Frost has adopted for the corresponding eclipse lines, 

 and the seventh the intensities of the lines reduced from the Kensing- 

 ton eclipse photographs. To make them roughly comparable with 

 Professor Frost's, these intensities have been multiplied by ten through- 

 out, as 1 is adopted for the weakest lines in the Kensington photo- 

 graphs, whereas he adopts 10 for lines just visible. 



