ASTRONOMICAL PROBLEMS— CURTIS. 333 



limit about 300 parallaxes have been determined, many of them a 

 number of times, by different observers and different methods. 



In the interesting field of double stars, as is well known, Herschel 

 discovered many systems in the southern skies, and modern observers, 

 as Innes, Taylor, and others, have materially augumented this num- 

 ber. During the past decade Profs. Aitken and Hussey have been 

 making a very complete and systematic search for such doubles in 

 the Northern Celestial Hemisphere, with the result that several thou- 

 sand new doubles have been discovered, many of them of great in- 

 terest. They have reached the conclusion that at least 1 in every 

 18 stars brighter than the ninth magnitude is a visual binary system. 

 To these results we must add the evidence of the spectroscope that 

 1 in every 5 or 6 of the stars thus far examined is a spectro- 

 scopic double, and we have facts whose importance it is scarcely 

 possible to overestimate in their bearing on our theories of stellar 

 evolution. Such systematic researches for the discovery of visual 

 doubles are most urgently needed in the southern skies to round out 

 the program which these astronomers have now nearly completed 

 for the northern portions of the heavens. In this regard there is no 

 doubt that the southern sky offers one of the richest and most promis- 

 ing fields of research existing to-day. Burnham's great " Catalogue 

 of Double Stars," recently published by the Carnegie Institution, 

 includes 13,665 pairs of stars and extends to south declination 31°. 

 This eminent authoritiy estimates that a century must pass before 

 sufficient data can be collected to make a similar catalogue necessary 

 for the Southern Hemisphere. Innes's " Reference Catalogue of 

 Southern Double Stars" 1 contains 2,191 pairs between the Equator 

 and the South Pole, but of this number about 925 are between the 

 Equator and Burnham's southern limit, nearly all of which have 

 been discovered by observers in the Northern Hemisphere. A com- 

 parison of the number remaining, south of —31°, with the results 

 from the northern skies will show clearly that there may well be 

 2,000 double stars brighter than the ninth magnitude at present 

 awaiting discovery in the Southern Hemisphere, to say nothing of 

 the need for additional researches on the pairs already known. 



During the past 10 years systematic observations have been made 

 at six special stations in the Northern Hemisphere to study the small 

 oscillations of the axis of the earth known as the variation of latitude. 

 These stations are located at Mizusawa, Japan; Tschardjui, Asiatic 

 Russia; Carloforte, Italy, and at Gaithersburg, Md. ; Cincinnati, 

 Ohio, and Ukiah, Cal. ; and are all situated almost exactly on the 

 parallel of north latitude 39° 8'. In 1905 the association which 

 has this research in hand, Das Centralbureau der Internationalen 

 Erdmessung, decided to extend this series of observations to the 



1 Cape Annals, vol. 2, pt. 2, 1899. 



