ASTEONOMY. 



201 



index to Chacornac's charts (including the later Paris charts) is pre- 

 sented : 



DOUBLE STARS. 



The long series of measures of double stars, made at Washington from 

 1875 to 1880, by Professor Hall, has been published separately. Pro- 

 fessor Hall has made a complete series of observations of a selected list of 

 doubles, selected by Dr. Struve and himself for comparison, and besides 

 has investigated the angles and sides of a triangle and a quadrilateral 

 of stars as measured and computed. The results of these measures are 

 excellent. The double stars measured are very numerous, and are nearly 

 all of interesting stars. A discussion of a two years' series of measures 

 on the trapezium of Orion is given separately, adjusted by least squares. 



The star C Cancri is triple and has been well observed. Dr. Seeliger, 

 of Leipzig, has investigated the orbits of the three stars. A, B, C, in a 

 memoir, of which he has given a synopsis in the Sltzungsberichte of the 

 Vienna Academy for May, 1881. Without giving details, we may state 

 his principal results. He first finds an orbit for B about A, and this 

 orbit satisfies the observations very well without taking into account 

 the star C at all. This may arise from one of two things : either the in- 

 fluence of C is veritably small, or the perturbations by C occur in such 

 a way as to compensate in their effects on the elements of the orbit of 

 B and A. Dr. Seeliger has shown that the latter is the case. For the 

 mass of C we can (arbitrarily) assume large values without destroying 

 the agreement between observation and computation, and iurtlier, he 

 has shown that a large value must be assigned to the mass of 0. This 

 lias been shown in different and indei)endent ways. The mass of C is 

 larger tban 2.4 times the sum of the masses of A and B. 



The orbit of C is next investigated, and a suggestion of Dr. Otto 

 Struve's that moves round a dark body near it, is found to be highly 

 probable. The final result of his discussion of this question is that it is 



