October 31, 1902.] 



SCIENCE. 



691 



with a view to increase the niimber of well- 

 determined stars near the pole. The great 

 scheme of the Astronomische Gesellschaft 

 of Leipzig for observing the stars of the 

 northern heavens down to the ninth mag- 

 nitude does not go beyond 80 degrees 20 

 minutes of north declination. The well- 

 known need of additional work— especially 

 fundamental work — in this part of the 

 heavens has led me to outline a plan for 

 fundamental observations of the circum- 

 polar stars, which has not, as far as I know, 

 been hitherto suggested or put into practice. 

 One of the chief difficulties in making 

 fundamental determinations of the right 

 ascensions of the stars at low declinations 

 is in securing sufficiently accurate time 

 keeping. This difficulty almost disappears 

 near the pole, where an error in time means 

 a much smaller error in space. The possi- 

 bility of making observations at both up- 

 per and lower culminations is an impor- 

 tant advantage in circumpolar work in both 

 right ascension and declination. Those 

 circumpolar stars which are bright enough 

 to be seen in the daytime with meridian in- 

 struments are frequently observed by as- 

 tronomers at both culminations at all times 

 of the year. During the fall and winter 

 months when in middle latitudes there are 

 from twelve to fifteen hours of darkness 

 daily, it is practicable to observe the 

 fainter circumpolar stars at both upper 

 and lower culminations. For six months 

 of the year it is possible to work for 

 an hour or two in the evening, be- 

 tween five and seven o'clock, observing a 

 certain list of circumpolar stars as they 

 come on the meridian at either upper or 

 lower culmination. In the morning, twelve 

 hours later, the same stars may be observed, 

 each at the other culmination. In this way 

 it is possible to observe with one instrument 

 in a single year, at both upper and lower 

 culmination, nearly all stars down to the 



seventh magnitude within ten degrees of 

 the pole. 



With a meridian circle provided with the 

 usual accessories, including suitable meri- 

 dian marks, the work may be made pract- 

 ically fundamental in both right ascension 

 and declination. The right ascensions of 

 ephemeris stars near the equator, used as 

 clock stars, are known with sufficient ac- 

 curacy so that the effect of their systematic 

 errors may be neglected without serious 

 error in observations of stars within 10 

 degrees of the pole. 



Each pair of observations of the same 

 star at both upper and lower culminations 

 on the same day gives a fundamental deter- 

 mination of the azimuth of the meridian 

 mark and the latitude of the place of ob- 

 servation, the observations in declination 

 being made from the nadir. The observa- 

 tions of each night should be reduced with 

 the azimuth of the mark and the latitude as 

 found from the observations of that night, 

 as in this way the effect of the recently 

 discovered slight motion of the zenith-point 

 is eliminated from the observed places. 

 The more troublesome errors of personal 

 equation will be eliminated from the final 

 results of a year's work. In declination, 

 the effect of errors of flexure of the instru- 

 ment and of the refraction tables will be 

 small. They will be somewhat smaller per- 

 haps the higher the latitude of the place. 

 Accidental errors of observation will be re- 

 duced to a minimum since the atmospheric 

 conditions are usually best in the early 

 morning and evening, and will be smaller 

 at the higher latitudes. Observations made 

 in this way will give the variation of the 

 latitude as well as its mean value, and also 

 the variation of the azimuth of the meri- 

 dian mark. By observing, in addition to 

 the circumpolar stars, stars which are se- 

 lected for the purpose, corrections may be 

 found to the refraction tables and to the 

 constant of aberration. 



