40 



KNOWLEDGE 



[Februaby 1, 1898. 



these objects were taken, are insufficient to show sensible 

 changes that may have taken place in their structures ; 

 but ere long such changes will inevitably be perceptible, 

 and the photographs will with certainty reveal their extent 

 and character. 



Who can say that a catastrophe, such as may have 

 produced any one of these nebulae, will not occur in our 

 time, and that we shall not be both eye-witnesses as well 

 as recorders of the beginning of another new spiral nebula, 

 in addition to the convincing evidence furnished by those 

 already published, showing the evolution of new stellar 

 systems by processes of disintegration and re -aggregation '.' 



MOON IN ECLIPSE, JANUARY 7, 1898. 



On last Friday night I was watching the eclipse of the 

 moon, and was struck with the density of the penumbra, 

 which prevented the outline of the earth's shadow being 

 distinguished. The penumbra also seemed irregular in 

 shape. As the night was fairly clear I took a photograph 

 with a twelve and a-half inch Calver's reflector, with one 

 of Browning's Kellner eyepieces. Time of exposure, one 

 and a-half seconds. L. Paxton. 



THE SPECTRA OF BRIGHT STARS.* 



By E. Walter Maunder, F.K.A.S. 



THERE is no branch of spectroscopy without its 

 charm, but the study of the spectra of stars has 

 an attraction all its own. Their hkenesses and 

 their difierences are so suggestive ; they hint at 

 so much of revelation as to the secrets of world 

 life ; they have, like an inscription in unfamiliar characters 



* "Annals of the Astronomical Obserratory of Harvard College," 

 Vol. XXVIII. Part I.— Spectra of Bright Stars photograplied with 

 the 1 1 -inch Draper Telescope as a part of the Henry Draper Memorial, 

 and discussed by Antonia C. Maury, under the direction of Edward 

 C. Pickering, Director of the Observatory, Cambridge, Mass. (John 

 Wilson & Sons, University Press. 1897.) 



and in an unknown tongue, so plainly a message to tell if 

 we could but interpret them. At such interpretation we 

 have indeed made our first attempts : the riddle is not all 

 unread ; we have spelled out a word — it may be even a 

 sentence — here and there, and, like Cleopatra's soothsayer, 

 can say : 



" In Nature's infinite book of secrecy 

 A little I can read." 



A little as yet ; still our knowledge grows, and the fullest 

 putting together of the starry hieroglyphs, the completest 

 alphabet yet formed from them, has just been laid before 

 us. 



This work, like so much in the same department of 

 astronomy that has preceded it, comes to us from the 

 Harvard College Observatory, and from that 

 section of it which the munificence of Mrs. Henry 

 Draper has enabled Prof. Pickering to develop. 



The great Draper Catalogue was the result of 

 a survey of all stars down to the eighth mag- 

 nitude, but the dispersion employed was neces- 

 sarily small, and only the most salient features 

 of the dill'erent spectra were brought out. 

 Volume XXVni., Part I., of the " Annals of 

 the Observatory " continues the photographic 

 study of stellar spectra, giving, however, but 

 six hundred and eighty-one stars as compared 

 with the ten thousand of the Draper Catalogue ; 

 but these have been photographed on so much 

 fuller a scale that our advance in the knowledge 

 of stellar constitution will owe far more to it 

 — and one cannot, indeed, help regretting that 

 the more special discussion had not preceded the 

 more general. 



The present survey is based upon examination 

 of some four thousand eight himdred photo- 

 graphs, representing the spectra of sis hundred 

 and eighty-one of the brightest stars north of 

 — 30^ declination. The instrument used was a 

 telescope of eleven inches aperture and a focal 

 length of one hundred and fifty-three inches, 

 used in connection with objective prisms in 

 number one to four, each of which had a re- 

 fracting angle of about 15^. The faintest stars 

 could, of course, be only photographed with one 

 prism ; the brighter were therefore photographed not only 

 with the highest dispersion they would bear, but in a 

 number of cases with one or two prisms for the sake 

 of better comparison with the fainter stars. The solar 

 spectrum was photographed for comparison with the same 

 telescope, combined with the Draper fifteen-inch reflector 

 used as a collimator. 



The detailed study of these spectra and their classifica- 

 tion has been the work of one lady. Miss Antonia Maury, 

 and has occupied her nine years. The most considerable 

 part of this great work is therefore hers alone, though the 

 takhig of the photographs, a large part of the determination 

 of the wave-lengths, and of the preparation of the volume 

 for publication, fell to other members of the stafif. 



A glance at Miss Maury's classification shows how 

 great an advance we owe to her. Secchi's types gave us 

 but a view of the most salient differences existing between 

 the stars. Vogel elaborated these considerably, and intro- 

 duced the important idea of a connection between the 

 type and the temperature of a star. His idea therefore 

 gave us a connected evolution along a single straight line. 

 Lockyer's classification was more elaborate, and was a 

 further advance — at least in so far that he introduced the 

 idea of rising as well as of falling temperature, and gave us 

 for his line of evolution not a single straight line, but a 



