Masterpieces of Science 



Fig. i the theoretical curve during December, 

 1889, is represented by the sinuous line, abscissas 

 indicating times, and ordinates the corresponding 

 separations of the components of the K line. 

 The black circles represent the twenty-seven 

 photographs taken during this month, their 

 ordinates representing the result of a rough 

 measure of the separation of the lines. In no 

 case does the observed position differ from that 

 given by theory by more than the accidental 

 errors of measurement. Fig. 2 is a contact print 

 from the original negative taken December 31, 

 1889, at nh. 5m., Greenwich mean time. Fig. 

 3 is an enlargement with cylindrical lenses of this 

 same negative. Fig. 4 represents a still greater 

 enlargement of the same negative,' and shows 

 the K line distinctly double ; by shading one part 

 of the photograph the strong line a to the left of 

 K is also shown in the enlargement to be double. 

 . Fig. 5 is a similar enlargement of a 

 negative taken December 30, 1889, at 17 h. 6m., 

 Greenwich mean time, eighteen hours previous 

 to Fig. 4. The lines here are single."* 



This subtile means of detection is set upon the 

 track not only of double stars, but on that of 

 such a star as Algol, which is attended by a planet 

 so large as to eclipse it almost wholly in a period 

 somewhat shorter than three days. 



"These binary systems, so different from any 

 previously known, would in all likelihood have 



* Henry Draper Memorial, Fourth Annual Report, Cam- 

 bridge, Massachusetts, 1890. 

 92 



