Absorption Markings in “K” Spectroheliograms

Abstract

MR. EVERSHED'S remarks in NATURE of May 11 cause me to think that possibly an essential difference in the method employed for reproducing original negatives for journalistic purposes might go far towards explaining the difference of definition and richness of detail in M. Deslandres' plates. Anyhow, we are now assured that the Kodaiknal negatives show in the main the same structures as those taken at Meudon. Yet if the former admittedly permit such a great amount of K₂ radiation to mingle with K₃, it seems to me risky to base certain reasonings on the appearance of the resulting spectroheliograms. Accepting Prof. Hale's interpretation, given now many years ago, that K₃ represents the highest level and K₂ an intermediate one, I submit that the Meudon plates are more likely to represent the true spectroheliographic aspect of the sun. It may be, as Mr. Evershed says, that the dark concentrations called fiocculi are entirely due to variations in the intensity of the narrow absorption line (or, in my opinion, rather the other way about); but is not this variation due, if not entirely, at least to a great extent, to the presence or absence or degree of intensity of the K₂ radiations on either side of K₃? A study of M. Deslandres' spectroheliograms taken on the sectional principle leads one irresistibly to think so. From the preceding remarks anyone can gather why I considered, and still do, the assumption of alternating appearance and disappearance of the large flocculus covering the range of prominences during March and April, 1910, rather unlikely.