464 
MR. J. EVERSHED ON THE SOLAR ECLIPSE OF 1900, MAY 28. 
and does not include lines (other than those of He and H) which are not present in 
the dark line spectrum. 
The most important point remaining open for discussion is the relation of the 
intensities of the bright lines to those of their dark line equivalents, for on this 
point turns the question whether the flash spectrum layer is in truth the stratum 
which by its absorption gives rise to the Fraunhofer spectrum. 
In discussing the results of the flash spectra obtained in India in 1898,"^ I stated 
certain conclusions leading to the belief that the flash spectrum does, in fact, 
represent the upper more diffused portion of an absorbing stratum which, taken as a 
whole, produces the Fraunhofer lines. The conclusions relating to the relative 
intensities of the lines I now recapitulate in the following three paragraphs :— 
(1) The relative intensities of the lines of any one element in the flash spectrum 
are practically the same as those of the same element in the solar spectrum. 
(2) The relative intensities between groups of lines belonging to different elements 
are widely different in the flash and in the solar spectrum. 
(3) The apparent intensity of the radiation from an element in the lower 
chromosphere is determined by the extent to which that element is diffused above 
the photosphere, and the real relative intensities between the different elements 
cannot be judged in photographs of the flash spectrum. 
The statements in the second and third paragraphs will now probably be generally 
admitted, and do not need further discussion. It remains to determine how fai' the 
statement given in the first paragraph is l:)orne out by the present results, which 
cover a somewhat different range of the spectrum, give more accurate values of the 
wave-lengths, and which give very much more complete and reliable values of the 
intensities of the lines. 
Probalfly this is the most important conclusion deduced from my former results, 
and as it is one which is most open to criticism, I propose to deal with it in some 
detail, and with especial reference to the results obtained by Fowler and Baxaxdall 
under Sir Norman Lockyer. These investigators have found that the relative 
intensities of the lines of an element in the flash approximate to those in the spark 
spectrum, whilst the intensities of the dark lines closely resemble those in the arc 
spectrum ; whence they conclude that the flash spectrum layer is not the seat of the 
Fraunhofer absorption lines.! 
In making comparisons of intensity in the lulght line and dark line spectra of an 
element, a serious difficulty is encountered in the probably compound nature of many 
of the apparently single lines of the flash spectrum. In such cases it is, of course, 
impossible to assign the true value of intensity to the components; even when the 
unequal components of an obviously double line are easily distinguished, it is difficult 
* ‘Phil. Trans.,’ A, vol. 197. 
t See Fowler on the Flash Spectrum, ‘ Observatory,’ April, 1902. Also Sir N. Lockyer and 
Baxandall, ‘ Monthly Notices, R.A.S.,’ vol. LXL, Appendix, 
