The Draper Catalogue

ON p. 133 of the current volume of NATURE (June 11) Mr. Espin gives a comparison of the Draper Catalogue of Stellar Spectra with the catalogues of Vogel and Dunér. Vol. xxvi. of the Harvard Annals, of which the first part will he distributed in a few days, discusses at length the deviations from Vogel and also from the similar catalogue of Konkoly. A second examination was made on photographic plates having a long exposure of those stars which appeared discordant. Since spectra of the first type pass by insensible degrees into the second, and these in turn into the third, no two observers would agree on the exact points of distinction. Moreover, different characteristics would distinguish the photographic and visual portions of the spectra (H. C. Annals, xxvi. pp. 177, 189). Some discrepancies, as in the case of the three fourth-type stars which are erroneously entered in the Draper Catalogue, are due to errors of identification (xxvi. p. 192). The photographic spectra of faint third-type stars are always indistinguishable from those of the second type (xxvi. p. 178). See also remarks following Table II. of vol. xxvii. The bright lines cited by Mr. Espin are probably portions of the spectra contained between dark bands or lines (xxvii. p. 3). Spectra are difficult to classify when measured as faint as 6.5; not when the final magnitude is brighter than 6.5, as might be inferred from Mr. Espin's reference (xxvii., preface).