134 ASTRONOMY FOR 1889, 1890. 



teui is 104 days. Wbeii oue component is approaching" tlie earth all 

 tlie lines in its spectrnni will be moved toward the blue end, wnile all 

 the lines in the s[)ectruni of the other conii)onent will be moved by an 

 equal amount in the opposite direction if their masses are equal. Each 

 line will thus be separated into two. When the motion becomes per- 

 pendicular to the line of sight, the si)ectral lines recover their true 

 wave-length and become single." 



From the amount of separation of the lines Professor Pickering con- 

 cludes that the relative velocity of the two comijonents must be about 

 100 miles per second. If the orbit is circular and its plane passes 

 through the sun, the distance traveled by one component, regarding 

 the other as fixed, would be 900,000,000 miles, and the distance apart 

 of the two components would be 143,000,000 miles, or about that of 

 Mars and the sun. The combined mass would be about forty times 

 that of the sun to give the required period. 



Several other stars have been found from the Harvard photographs 

 with a similar doubling of the lines, among them fi Aurigne and h 0[»hi- 

 uchi. For /S Aurigse Professor Pickering deduced a period of 4 days, 

 and his results have been fully confirmed by observations made with 

 quite diflerent apparatus by Dr. Vogel at Potsdam. 



A doubling of the K line in several photographs of the spectrum of 

 Vega taken by Mr. A. Fowler, apparently indicating that Vega was a 

 double star of the C Ursfe Majoris type, has not been confirmed by the 

 photographs of Pickering, Vogel, and Henry. 



The Henry Draper Memorial.- -The third annual report of Professor 

 Pickering announces the practical completion of two bi-anches of the 

 work undertaken, the photographic survey of the spectra of all stars 

 north of — 25° declination having been effected on a twofold scale, the 

 one survey including all stars brighter than the seventh magnitude, the 

 other including stars two magnitudes fainter. The Bache 8-inch doub- 

 let employed in this work has been transferred to a station near Chos- 

 ica in Peru and similar surveys for the stars down Ito the south pole 

 have been commenced. 



The fourth annual report of the Henry Draper Memorial contains as 

 a frontis piece an engraving showing the periodical duplication of the 

 K line in the spectrum of fi Auriga?, the study of which, with other 

 similar cases has been the most important work of the 11-inch equa- 

 torial at Harvard. The spectroscoi)ic survey of the brighter stars 

 in the northern hemisphere (to — 25° declination) is nearly printed 

 and the work on fainter stars is being satisfactorily pressed. Besides 

 the spectra, charts of the entire sky are being formed with the same 

 telescoi)es. A photograj^hic map of the sky will thus be provided, ap- 

 proximately on the scale of the Durchmusterung, but including fainter 

 stars; so far as it has been comi)!eted it has proved very convenient 

 for studying suspected variables and in detecting errors in star cata- 

 logues. 



