88 PRESIDENT S ADDRESS SECTION A. 



revealing a number of additional lines in the ultra violet as well 

 as in the continuous spectrum, and he considered it probable that 

 these features indicate a physical condition at or near the beginning 

 of the cycle of their celestial evolution. 



The white stars are distinguished by the number of their spectra 

 lines in the ultra violet, Avhich indicate a greater intensity of tem- 

 perature and point to a comparatively recent formation from the 

 condensation of highly heated matter; as these stars radiate their 

 heat they change color, the red stars being the coldest we know. 



In 1890 the southern part of the Milky Way was photographed 

 at Sydney with a 6in. protrait lens, special attention being given to 

 to the parts that are dark to the eye. and the camer.-i revealed a 

 multitude of stars in them, especially in the Coalsack in Crux, in 

 which the stars seemed about as numerous as in the pans about, 

 and their distinctive grouping has such a strong family likeness to 

 the parts of the Milky Way near them that there seems to be no 

 reason to doubt they belong to the same system. 



In August, 1889, Professor Pickering'" pointed out that u star 

 camera with double objective 24in. in diameter would be a power- 

 ful aid to astronomical photography, and Miss C. W. Bruce, 

 of New York, came forward and gave 50,000 dollars for the pur- 

 pose of making this great instrument for photograj^hing star 

 spectra. On January 8th, 1890, Professor Pickering"' announced 

 that one of the results of the work done under the Draper Memorial 

 was the discovery of a new class of binary stars, whose components 

 are far too close to be seen hj any other method. 



It was first noticed that the conspicuous lines in the star were 

 sometimes double, and an extended series of photographs revealed 

 the fact that the duplication came at intervals of fifty- two days, 

 and this is completely accounted for if one assumes the existence 

 of two stars with similar spectra very close together and revolving 

 round each other in a plane passing nearly through the sun ; the 

 doubling of the line is, of course, caused by the fact that the star 

 is at one time moving towards us and at another away from us. A. 

 similar case was discovered by Miss A. C. Maury, who, when 

 examining the photographed spectra of Beta Aurigse on forty- 

 seven photographs, found that the star line doubled periodically 

 like those in Zeta Ursse Majoris, hut at shorter intervals ; in fact, 

 that one of the stars goes round the other in two days. It is a 

 startling discovery to find binary systems of this kind so very 

 different from any previously known, and I think there can be no 

 doubt that this fact would have been hidden for ages to come but 

 for photography, because until the discovery was made there was 

 no apparent reason for every day examination of the spectrum of a 

 star ; indeed, until then, when the lines were once carefully mea- 

 sured they were put aside by the observer as finished and definite 

 records of the star's spectrum. These first results indicate that the 

 components of Beta Aurigse are separated by an angular interval of 



