4.68 Scientific Proceedings, Royal Dublin Society. 
12. Double Stars. 
In 1841 and 1842 the Pulkova refractor was used for an exami- 
nation of the northern hemisphere in search of double stars. 
The second part of the catalogue thus formed embraces systems, 
the components of which are of or above the eighth mag., and 
the distance between which are from 32" to 2’. Most of these 
objects have never been observed micrometrically, and the series 
of heliometer measures of some of them, which Dr. Schur of 
Strassburg publishes in the A.N. 2255-56, will therefore be of 
interest, though only comprising a small number of objects. 
Systems closer than 40” were measured by quadruple distances, 
wider pairs by double distances. By means of an artificial pair 
of stars, it was found that the position angle had no appreciable 
influence on the measures of distance, and that the two methods 
of measuring the distances showed no constant difference. 
Volume XLIV of the Memoirs R.A.S. contains a very extensive 
work by Mr. Burnham: “Double Star Observations made in 
1877-8, at Chicago, with the 182-inch refractor of the Dearborn 
Observatory, comprising: I. A Catalogue of 251 New Double 
Stars with Measures; IJ. Micrometrical Measures of 500 Double 
Stars.” 
Up to a few years ago the Dearborn refractor, with which 
Clark discovered the companion of Sirius in 1862, was kept 
perfectly idle, the original dome being a mechanical failure, only 
fit to act as an extinguisher. It has however, since, in the hands 
of Mr. Burnham, done excellent work. Confining himself to the 
subject of double stars, this distinguished observer has in the 
course of six or seven years, first working with a 6-inch, after- 
wards using the 183 i. refractor, made this subject his own to an 
extent which 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 labour expended. 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, « Lyre may 
be cited asexamples. Couples which small instruments of three or 
