ASTRONOMY. 



109 



science. M. Bigourdau reviews the work of others in this field, gives 

 a description of apparatus which he lias devised for investigating the 

 problem by means of artificial stars, and deduces liis own personal 

 equation from a large number of measures made with this apparatus. 

 He finds that his i^ersonal equation is not affected by the position of 

 the eyes with respect to the line joining the stars nor by the altitude; 

 the brightness of the stars, on the other hand, does affect his measures. 

 The second paper referred to is by Mr. H. C. Wilson, formerly of the 

 Cincinnati Observatory, and is published iu the Sidereal Messenger 

 (vol. 5, pp. 174, 211). Mr. Wilson gives an interesting sketch of the 

 history of the subject, together with an investigation of his personal 

 errors, obtained from observations made between 1882 and 188G, with 

 the equatorial of the Cincinnati Observatory. He finds tliat his meas- 

 ures, both of position angle and of distance, are slightly influenced 

 by the inclination of the head. 



Spectroscopic metlwtl of determining the distance of a double star. — Mr. 

 A. A. Eambaut, of the Dublin Observatory, in a paper communicated to 

 the lioyal Irish Academy on May 24, 188G, discusses at some length the 

 possibility of determining the distance of a double star by measures of 

 the relative velocities of the com}»onents in the line of sight. Dr. 

 Huggins having demonstrated that it was practicable to measure the 

 rate of approach or recession of a star, it was seen that it would be 

 at least theoretically {)ossible to determine the distance of a star by 

 this method. Mr. liambaut's critical examination of the conditions of 

 the problem shows however that the method can have but little prac- 

 tical application. 



Orbits of double stars. — The following table gives the " period of revo- 

 lution" in years, and "semi-axis major," in seconds of arc, obtained for 

 a number of binary stars in recent determinations of elements : 



VARIABLE, NEW, OR TEMPORARY STARS— COLORED STARS. 



Observations of variable stars in 1885. — Professor Pickering prints in 

 the twenty-first volume of the Proceedings of the American Academy 

 his third annual report upon observations of variables, giving particu- 



