March 20, 1885.1 



SCIENCE, 



241 



RESEARCHES IN STELLAR PARALLAX. 



The observatory of Trinity college, Dublin, 

 has long been the most famous spot on earth 

 for determinations of stellar parallax ; and the 

 labors of the present astronomer royal of Ire- 

 land, Dr. Ball, conducted in the same line of 

 research, will make good the claim of this 

 institution to such distinction for a long time 

 to come. Before the time of Dr. Briinnow, 

 formerly astronomer royal at Dunsink, no as- 

 tronomers had, except in isolated instances, 

 attacked the problem of stellar parallaxes for 

 its own sake ; that is to sa} T , the determina- 

 tions of parallax had come about rather inci- 

 dentally, and had not been undertaken with 

 the idea of determining stellar distances as the 

 sole end of the research. The painstaking 

 care which Dr. Briinnow exercised as an ob- 

 server, and his conscientious thoroughness in 

 the subsequent numerical work based on his 

 observational data, were so skilfully combined 

 as to show that the distances of the stars were 

 reacliry determinable with a hopeful, and to 

 a certain extent satisfactory, precision. The 

 stars with which he was largely occupied were 

 a L}Tae, Groombridge 1830, 85 Pegasi, and 

 8 Draconis. 



Dr. Ball, appointed astronomer royal some 

 ten years ago, has wisely devoted the resources 

 of the Trinity college observatory in the main to 

 parallax research, and he has greatly amplified 

 the plans of his predecessor. In the present 

 volume he details the method by which his ob- 

 servations in systematic search for stars with 

 a large parallax have been conducted ; and it 

 is plainly apparent how an enthusiastic worker 

 can completely observe so many stars when 

 special pre-arrangements are adopted for the 

 economy of time and labor. With slight 

 changes, these same methods would be equally 

 applicable to the details of other observatory 

 work, and would result in an equal saving : the 

 methods are quite similar to those now so com- 

 mon in the details of library management, and 

 have already been adopted by many astrono- 

 mers in facilitating their work. 



It will be a matter of interest to many to 

 know how, from the myriads of stars in the 

 sky, Dr. Ball was guided in the selection of a 

 list embracing about a thousand objects. In 

 the first place, only such objects were taken as 



Astronomical observations and researches made at Dunsink. 

 Fifth part. Observations in search of stars with an annual par- 

 allax. By Robert S. Ball, LL.D., F.R.S., astronomer royal. 



Heliometer determinations of stellar parallax in the southern 

 hemisphere. By David Gill, LL.D., F.R.S., her Majesty's as- 

 tronomer at the Cape of Good Hope, and W. L. ELKiN,'Ph.D. 

 Forming part i. of the forty-eighth volume of the memoirs of the 

 Royal astronomical society. 



were included between 30° and 65° of north 

 declination, and every object of importance in 

 Admiral Smyth's celebrated cycle of celestial 

 objects was transcribed into the working-lists. 

 Struve's catalogue was also drawn upon, and 

 likewise catalogues of red stars by Schjellerup 

 and Birmingham ; the hypothesis with regard 

 to objects of this type being that their color 

 may be due to their small size, and thus pre- 

 sumably less far removed from the solar s}'s- 

 tem. A number of the variable stars, also. 

 are probably ver} 7 small, and they were included 

 in Dr. Ball's lists for a like reason. 



It will not be understood that Dr. Ball's 

 work amounts to a conclusive determination 

 of the distances of all these objects : the ob- 

 jects of his research are at present very differ- 

 ent from this ; and his labors were directed 

 with main reference to a decision, in all cases, 

 whether the observed stars indicate a suffi- 

 ciently large parallactic displacement to merit 

 further immediate attention. Of course, there 

 was no disappointment in finding that a very 

 small proportion of the objects examined gave 

 satisfactory evidence of a measurable parallax ; 

 but the labors of Dr. Ball are none the less 

 important to future observers as indicating 

 clearly the direction in which there is no 

 pressing need of similar investigation. So 

 much for the inconclusive part of this work. 

 And we may now speak of the positive results 

 in the shape of accurate determinations of the 

 parallax of 61 (B) Cygni, Groombridge 1618, 

 and 6 Cj'gni (B). 











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PARALLAX IN DECLINATION OF 61 (b) CYGNI. 



The first star belongs to the famous binary 

 s} 7 stem, the first determination of whose dis- 

 tance was made b} 7 the illustrious Bessel ; and 

 Dr. Ball finds its annual parallax to be very 

 little short of half a second of arc. In order 

 to show the degree of accuracy- attained in 



