pko(;ki:ss of astronomy for isiti and isii2. (i89 



I'rof. L'ickciiiiii- has iiioro icceiitlx' calh-d attoiitioii t<» aiiotlicr 

 iiitercstiii.ii' class (»f ••iii\isil)l(' (l()iil)l(' stars," dctocted in a soiiicwliat 

 similar way 1)\' peculiarities in tlieir sjx'ctra. 



Of many douhle stars the briiiliter c<»mi»()neiit is red or yeUow. MJiih' 

 the fainter conii)()nent is iireen or blue. The s])ectr()sc()]>e sliows that 

 this is due to the fact tliat thesi>ectrnm of the brii^hter <'<)in})onen{ is of 

 tile second type, like our sun, while the S])e(;trum of the fainter coiupo- 

 nent is of the lirst type, traversed by shonyly marked hydrogen lines. 

 If the stars arc ue;ir together the spectrum of the combined light re- 

 sembles that of the sun, except that th<> hydrogen lines are all strong. 

 Stars like /> Cygni give such a spectrum, but the components are so far 

 ai)art that the separation of their six'ctra is clearly shown. Se\-eral 

 stars hitherto supposed to l)e single have been found whose spectrum 

 is of the class descrilx'd above, ami the ([uestion arises whether they 

 may not really be double with components so clos<>that they can notI)e 

 se})arated by ordinary means. In the detailed exaniination of the spec- 

 tra of the brighter stars made by JNliss Ma.uiy upon the Harvard photo 

 graphs, stars occui)ying all internu'diate grades from the tirst to the 

 second type have been found, and it is diflicult to deternnne whether 

 there are really two spectra or merely changes in the spectrum of a sin- 

 gle star due to i)hysical causes. Tpon the hypothesis of du])licity the 

 hydrogen lines would probably show a ])erio(lic dis[)lacement, and in 

 fact an examiimtion of four photographs of the spectrum of l*rocyon 

 does show a displacement of tlu^ lines which, if the ])henomenou is due 

 to the relative mo\cinent of a faint <'omponent, would seem to indicate 

 that it is receding at the rate of UO kilonu'ters per second as compared 

 with the bright com[)()nent. Tln^ evidence of dui)licity is not con- 

 sidered conclusive by Prof. Pickering, ]»ut, from an examination of ten 

 other stars having a similar composite si)ectruin, live are w(dl-knowii 

 doubles, two have distant c()mi)anions, leaving three, r Persei, 

 Z Auriga', and rJ Sagittarii, which it wouhl seem from the above (;onsid- 

 (irations nuiy ])ossibly be double. 



VAIMAULJ', SIAUS. 



Alfjifl. — Mr. Chandler has published the results of an interesting 

 investigation of the variable star Algol, the periodicity of which ai>- 

 pears to ha\(' been lirst disco\<M-ed by ( loodricke. at York, in 17Sl!; and 

 the explanation suggested by him ol'the j)eriodic diminution of tiu' 

 brightness, that it is produced by the intei-|)osition o!' an oj>aqu«' sat- 

 ellite, is now generally accc|»tcd. coniirnied as it has recentiy been, by 

 tite investigations of I'rof. \ Ogel. Mr. rhaudler. alter an elabcuate 

 investigationof the imMjualities in the i>ei iod.and also of t he incgularity 

 in the observed proper motion of Algol, has found that they may bo 

 satisfactoril.N' accounted for b>- supi>osing that both Algol itself and th(i 

 satellite which icxohcs round it in about 1* days L'O.S hours have a 

 '•omiuon re\<)lution rouml a third, large, (|istant antl opatpi;- l)ody, in a, 



n. Mis. 114 — u 



