190 ASTRONOMY. 



at Chicago, with the 18i-inch refractor of the Dearborn Observatory, 

 comprising: I. A Catalogue of 251 New Double Stars with Measures; 

 II. Micrometrical Measures of 500 Double Stars." 



Up to a few years ago the Dearborn refractor, with which Claek 

 discovered the companion of Sirius in 18G2, was idle. It has, however, 

 since, in the hands of Mr. Burnham, done excelleut work. Confining 

 himself to the subject of double stars this distiuguished observer has, 

 in the course of six or seven years, first working with a 0-inch, after- 

 wards using the 18^^ inch refi"actor, made this subject his own to an ex- 

 tent that is truly surprising. Though many observations are yearly 

 being taken of double stars by a good many observers, the study of 

 these important objects is by no means being furthered to the extent 

 one should have expected from the vast amount of time and labor ex- 

 pended. As Mr. Burnham justly remarks, in the preface to the paper 

 we are here considering, many observers have gone on from year to 

 year observing over and over again the same familiar stars, of which 

 Castor, y Virginis, e Lyrae may be cited as examples. Couples which 

 small instruments of three or four inches aperture would show suffi- 

 ciently well are thus again and again being observed with fine refrac- 

 tors of six or seven inches aperture or upwards, while a very great 

 number of stars are hardly ever if at all looked for. " Omit the observa- 

 tions of Dembowski and O. Strute and our knowledge of nine-tenths 

 of the double stars would not be materially advanced in the last thirty 

 years." Mr. Burnham has from the beginning shown that he does not 

 follow the ordinary beaten track, and his numerous discoveries of close 

 and difficult i^airs have proved him to be an unusually sharp-sighted 

 and attentive observer. In nine previous lists he had given the places 

 of 482 new double stars, mostly rather difficult pairs, which few would 

 have discovered with a 6-inch refractor. The present (tenth) list of 251 

 new objects raises the total number of new double stars discovered by 

 Mr. Burnham to 733; of these 251 stars, 75 pairs are less than \" apart. 

 His observations of old double stars embrace chiefly such ones which 

 require a large aperture to be brought out well, or which have not been 

 recently observed by others. Particular attention has also been paid to 

 certain diificult pairs discovered by Mr. Alvan G. Clark. 



No. 5 of the i^ublications of the Cincinnati Observatory contains "Mi- 

 crometrical Measurements of 1,054 Double Stars from January 1, 1878, 

 to September 1, 1879." Though the discovery of new double stars has 

 only been considered a secondary object, nearly 200 new pairs have been 

 detected during the progress of the work at Cincinnati. The measures 

 are all given in full detail and occupy 151 pages; the mean results are 

 given separately. 



The systematic errors in measures of double stars have been investi- 

 gated by Professor Thiele in a paper: "Castor, Calcul du mouvement 

 relatif et Critique des observations de cette etoile double." (Copen- 

 hagen, 1879.) The author has chosen Castor partly because the orbital 



