Ball — Researches on Annual Parallax. 



355 



LIX. — Eeseaeches on Annitai Paeaxlax, made at Dttdtsink. By 

 EoiffiET S. Bail, LL.D., F.R. S., Royal Astronomer of Ireland. 



[Read, January 10, 1881.] 



In the following Paper I give a brief sketch of some of the observa- 

 tions which have been made at Dunsink during the last two or three 

 years. The full details will appear in the pubKcations of the Obser- 

 vatory, Part V. Some of the results have already been recorded in 

 the Journals which are more specially devoted to Astronomy (see Jfow^A/'y 

 Notices, R.A.S., JS'ov. 1880, Jan. 1881, and Urmiia, No. 1). The three 

 objects to which I wish to draw attention are the stars known as 

 61 Cygni, P m 242, and Groombridge 1618. 



(61 Ctgni). 



In 1838 Bessel commenced a series of measures from the central 

 point between the two components of 61 Cygni to the two other stars 



'(&)BESSEL 



,^©BESSEL 



JS38^-"" , 

 JSS3 ^ 



I8]8 6 •::::::---- 



Fig. 1. — 61 Cygni and Comparison Stars. 



a and I (see Pig. 1). « is a star of the 8*8 "mag., and is known as 

 BD + 37°, 4173 ; while Hs a star of the 8-6 mag., known as BD + 37°, 



n. I. A. PROC, SEE. II. VOL. III. — SCIENCE. 



2 F 



