Nature . of the stars of intermediate temperature, likea Cygni, have long been recognised by the Harvardobservers as well as by myself as presenting greatdifficulties. In 1893 I wrote as follows : With the exception ofthe K line, the lines of hydrogen and the high tempera-ture line of magnesium at \4481, all the lines maybesaid to be at present of unknown origin. Some of thelines fall near lines of iron, but the absence of thestrongest lines indicates that the close coincidences areprobably accidental. In the Harvard Spectra of BrightStars, 1897, p. 5, the following words occur, relating tothe
Nature . of the stars of intermediate temperature, likea Cygni, have long been recognised by the Harvardobservers as well as by myself as presenting greatdifficulties. In 1893 I wrote as follows : With the exception ofthe K line, the lines of hydrogen and the high tempera-ture line of magnesium at \4481, all the lines maybesaid to be at present of unknown origin. Some of thelines fall near lines of iron, but the absence of thestrongest lines indicates that the close coincidences areprobably accidental. In the Harvard Spectra of BrightStars, 1897, p. 5, the following words occur, relating tothe same stars : This system of lines should perhaps beregarded as forming a separate class, as in the case ofthe Orion lines, and should not be described as metallic,as has just been done in the absence of any more dis-tinctive name. From the fact that these unknown lines have now beentraced to a proto-metallic origin, as effectively as theunknown lines of the hottest stars have been traced to 39338 .4219-0. of a Cygni and the enhanced lines of (A = spectrum of a Cygni betweeti wave-lengths stated. etals (chiefly of the iron group).B = spectrum of enhanced lim The observations have already been mapped for thefollowing substances :— Iron, manganese, nickel, cobalt, magnesium, chromium,?calcium, strontium, copper, vanadium, titanium, silicon. In the accompanying photograph, a comparison isshown between the lines of a Cygni and the enhancedlines of the above substances thrown together. The ex-traordinary number of coincidences is seen at a facts are as follows :— The number of lines measured in the spectrum of aCygni at Kensington between \379Si and A4S61 6 is ... 307 Of these the number which approximately coincides with the enhanced metallic lines so far observed is 120The number of lines (excluding the hydrogen series) ina. Cygni of intensity over 4 (the maximum being represented by 10) is 40 Of this number, the coincidences with enhancedmetallic lines
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