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DR. T. R. MERTON AND MR, S. BARRATT 
A5552-52 enhanced by condensed discharge. 
A5543-41 
A5317-90 high pressure line. 
?? 
5 ? 
“ Low Pressure ” lines are weakened by the condensed discharge, which enhances the 
“ High Pressure ” lines, and the lines which are enhanced by the condensed discharge are 
also enhanced to a smaller extent by admixture of Helium ; but there are exceptions, 
and the changes in intensity amongst the lines which do conform to these rules vary 
greatly in magnitude. We are inclined to the view that many of the exceptions may 
be explained by the assumption that the exceptional lines are in reality close unresolved 
doublets. 
With regard to the lines showing the Stark effect, this attribute appears to bear no 
relation to any of the other methods of classification, but attention may be drawn to 
lines at A A 4185-4, 4123-9, 4021-7, 3927-3 and 3846-0, which are described as showing 
the Stark effect, but which do not appear on any of our plates. If these lines are indeed 
Hydrogen lines, it is possible that they make their appearance only in the powerful 
electric fields which are necessary for the investigation of the Stark effect. 
(6) Comparison of the Secondary Hydrogen Spectrum with the Solar Spectrum . 
The presence of lines of the secondary Hydrogen spectrum in celestial spectra has not 
been established, but in view of the fact that we have separated the secondary spectrum 
into groups, which vary in intensity under different physical conditions, we have made 
a careful comparison of a number of secondary lines with Rowland’s solar wave-lengths, 
and with the sun-spot lines recorded by Hale and Adams (' Astrophys. Journ.,’ vol. 23, 
p. 11, 1906). The most prominent lines of each class amongst the secondary lines were 
selected and were reduced from International Units to Rowland’s scale of wave-lengths. 
A table showing the comparison would be redundant, but it may be stated that there 
are very few coincidences within the limits of experimental error, and these coincidences 
appear to be accidental, for the relative intensities of the lines which might seem to be 
represented are not in harmony with their intensities on any scheme of classification 
which has been found. It is therefore probable that the secondary spectrum is not 
represented in the solar spectrum, though the range of wave-lengths relating to the 
sun-spot spectrum is not as great as might be desired. 
(7) The Widths of Spectrum Lines. 
In a previous section we have referred to the widths of spectrum lines and to their 
importance in setting an inferior limit to the molecular weight of the radiating particles. 
The distribution of intensity in a spectrum line, in the case in which the sole cause of 
broadening is that due to the motion of the radiating particles in the line of sight, is 
