260 S.C. Draper—Dark Lines in the Solar Spectrum. 
the position, and the horizontal portion the width, 
and also the darkness on an arbitrary scale of one to ten. The 
darkest lines encroach most on the vertical portion of the sym- 
bol. value 10 is expressed in the symbol of the Mn Fe 
line 4068, and the value 1 in that of the line 4068-05. 
Other features of the lines are shown by the manner in which 
the upper part of each of these symbols is drawn. Beneath 
the spectrum lines the scale is repeated, and the position of the 
oxygen lines indicated. In addition to the lines already men- 
tioned as being in Angstrém’s chart, lines of the following 
elements appear in this space, viz: Fe 4063, Pb 4066, Sr 
4078, Bi 4080. he correspondence between these values and 
the wave lengths of the lines in the photographic spectrum is 
as lose as could be expected, seeing that the authorities do 
absorbing power in the gaseous non-metallic elements, as com- 
pared with the same power in the case of metals in the vapor- 
ous state. The existence of a difference like this would ex- 
plain why it is, that many of the lines in the solar spectrum 
which represent oxygen have been overlooked. Some of these 
lines have, however, been observed, Angstrém himself giving 
in his chart a number of lines, not assigned by him nor any 
a 
