( 446 ) 
Physics. — “On the origin, of the chromospheric light.” By Prof. 
W. H. Julius, 
In a paper, entitled: Photography of the “flash” spectrum without 
an eclipse *), Hale and Adams conclude from their wavelength meas¬ 
urements in the regions X 4492— X 4584 and X 5111— X 5198 that 
the chromospheric lines coincide very closely in position with the 
Fraunhofer lines, as measured by Rowland. The average difference 
— taken without regard to sign — between the wave-lengths of 
121 chromospheric lines and those of the corresponding Fraunhofer 
lines, was found to be only 0.013 A ; and if the sign was retained, 
the average systematic deviation came out -j- 0.002 A, which was 
much less than the error of measurement. 
These provisional results are stated by them to be opposed to my 
hypothesis, according to which the bright lines of the spectrum of 
the chromosphere and the flash are mainly due to anomalous refrac¬ 
tion of light coming from the photosphere. They say : “If this were 
the case, however, we should expect their wave-lengths to differ 
appreciably from their normal values, being somewhat increased on 
the usual assumption of a density gradient decreasing outward from 
the surface of the sun.” 
In order to recall to mind the particulars of that anomalous refrac¬ 
tion theory, Hale and Adams refer to a paper by Hartmann (Astron. 
Nachr. 175, S. 347, 1907). I am under the necessity of also referring, 
for the same purpose, to the first article in which I started the idea 
that anomalous dispersion might be an important factor in producing 
solar phenomena * * 3 ); for Hartmann, in his criticism, does not do full justice 
to the argument there developed. Indeed, Hartmann puts it 3 ) as if I 
had overlooked a simple consequence of my own assumptions, viz. 
that, if the chromospheric light were due to anomalous refraction in 
a mass of gas, the density of which gradually decreases outward, 
only R-light 4 ) could appear in the spectrum of the chromosphere. 
Evidently, however, I was fully aware of that consequence, as this 
very consideration induced me to think, that to the appearance of 
the chromosphere and its spectrum the irregular anomalous refraction 
*) George E. Hale and Walter S. Adams, Gontrib. from the Mount Wilson 
Sol. Obs. No 41; Astroph. Journ. 30, Oct. 1909. 
2) Julius, Proc. Roy. Acad. Amst. II, p. 575 (1900); Astron. Nachr. 153, S. 433 (1900). 
3 ) Hartmann, Astron. Nachr. 175, S. 349 (1907). 
4 ) By R-light and V-light we indicate waves, lying very near an absorption line, 
on its red and its violet side respectively. 
