The chairman has kindly encouraged, not to say entreated, me to write a few remarks concerning the subject of your symposium, which I was unfortunately unable to attend. This I am happy to do: the hydrogen-deficient stars are dear to my heart and even though I haven’t contributed anything to the subject for several years, it is certainly nice to be remembered. From an outsider, then, a few thoughts.
To quote from Miss Payne, in her classical study of 1925: The uniformity of composition of stellar atmospheres appears to be an established fact.” Certainly for the time that statement was beyond reproach. Yet even then the seeds of hydrogen deficiency had already been sown. Mrs. Fleming, in noting the presence of bright Hβ in u Sagittarii, in 1891, further states that its spectrum “is remarkable, since the hydrogen lines are very faint and of the same intensity as the additional dark lines.” Further, Ludendorff, in a paper written on Aug. 16, 1906, discovered the complete absence of the Hγ line in R Coronae Borealis (a similar situation with respect to Hβ and Hδ being confirmed by Frost). And by a remarkable coincidence, a Harvard objective-prism plate taken the very same day was described by Miss Cannon as showing very little absorption at the G band. Both HD 30353 and RY Sagittarii are stated in the Henry Draper Catalogue to show a spectral resemblance to R CrB. And finally, the non-typical weakness of the G band of the carbon star HD 182040 was pointed out by Rufus as early as 1923.