90 THE CHEMISTRY OF THE SUN. [CHAP. 



The table of coincidences referred to, and Angstrom's remarks 

 thereon, explain the cause of this. Kirchhoff's evidence for zinc 

 had depended upon the coincidence of two lines only, and these 

 were doubtless thought insufficient, as in the cases of the 

 metals retained in the list the number of the coincidences was 

 much greater. 



From Angstrom's remarks, which I proceed to give, it is 

 evident that he was not quite satisfied with the brilliancy test 

 relied on by Kirchhoff, and that his doubts concerning zinc 

 arose from this cause. 



Of aluminium he writes l that although it gives brilliant lines 

 in different parts of the spectrum, yet the two lines situated 

 between Fraunhofer's two H-lines are the only ones which appear 

 to coincide with solar ones. By way of explanation of this 

 phenomenon he points out that the violet rays are much the 

 strongest in the spectrum of this metal. He observes that 

 these two lines often present the same phenomenon of absorp- 

 tion as is shown by the yellow sodium lines, which is a proof 

 of their great intensity. He states finally that the point will 

 be cleared up by ascertaining whether the ultra-violet lines 

 of aluminium coincide or not with faint solar lines in that 

 region. 



Of zinc he remarks 2 that the two lines he has given of that 

 metal as coincident with solar lines do not correspond with the 

 latter in character, being wide, very strong and nebulous, so that 

 the presence of zinc in the sun remains doubtful. It is note- 

 worthy, however, that there are three lines in the magnesium 

 spectrum which present the same nebulous appearance, and to 

 which there are no corresponding solar lines, and yet magnesium, 

 he thinks, is undoubtedly present in the sun. 



Angstrom intended to supplement his normal solar spectrum 

 with a series of maps of the bright lines of all the metallic 

 elements on a wave-length scale, but circumstances prevented 



1 Loc. cit. p. 36. 2 Idem. 



