692 



SCIENCE. 



[N. S. Vol. XVI. No. 409. 



The clock should be a good one, but need 

 not be of unusual excellence. The instru- 

 ment should be of the best quality, and its 

 errors in both right ascension and declina- 

 tion should be investigated as completely 

 and as rigorously as possible. The work 

 should be done in both positions of the 

 clamp of the instrument, and with the ob- 

 ject glass and eye-end interchanged. All in- 

 strumental constants should be determined 

 when the observations are made. In short 

 all expedients should be resorted to to 

 eliminate accidental and systematic errors 

 — especially the latter— as it is only in this 

 way that fundamental work can be made 

 of value as such in the present state of 

 astronomy. 



The observations may be corrected for 

 clock and instrumental error by either 

 Mayer's or Bessel's formula. If the latter, 

 which is perhaps the more convenient of 

 the two, is used it may be put in the form, 



a= T+ d T-l-m+ (n + e) tan d 



-f- c (see 5 — tan S) 



in which the quantity n is computed from 

 values of the level constant found with the 

 spirit level and a from observations on 

 the meridian mark. The term c (sec 5 — 

 tan s) may be used in the forms c/(sec S -j- 

 tan S) if more convenient. As is the case 

 with all astronomical work, the value of the 

 results will depend on the perfection and 

 power of the instrumental outfit, and the 

 skill with which the various processes are 

 carried out. This plan of observation is 

 of course applicable to the southern as well 

 as to the northern circumpolar stars. 



It may not be out of place to speak in 

 this connection of the need of an extended 

 series of fundamental observations of the 

 brighter stars at all declinations, to supple- 

 ment the work being done at Greenwich and 

 Pulkowa. Astronomers who are interested 

 in this subject feel the desirability of such 

 an addition to the material at present avail- 



able, from which to construct a general cat- 

 alogue of several thousand stars whose 

 places are based on an absolute system. The 

 stars should be selected with reference to 

 distribution, magnitude, color and other 

 characteristics which affect their suitability 

 to serve as standard points of reference. 

 Such a catalogue is needed for a variety of 

 purposes, among which may be mentioned : 



1. As a basis for determining the posi- 

 tions of the fainter stars, by differential 

 meridian circle observations or by photog- 

 raphy. 



2. For more convenient and accurate de- 

 termination of longitude and latitude in 

 geodetic work. 



3. To make possible a more accurate and 

 extensive determination of the proper mo- 

 tions of the stars in all parts of the heavens, 

 which together with spectroscopic measure- 

 ments of motions in the line of sight, likely 

 to be greatly increased in the near future, 

 will increase our knowledge of the proper 

 motion of the solar system and also the 

 motions and distribution of the stars in 

 space. 



4. To serve as a ^^niversal standard to 

 which the great mass of existing star-cata- 

 logTies, systems of star-places and series of 

 observations may be reduced by the appli- 

 cation of systematic corrections, thus har- 

 monizing and making available for use a 

 large amount of nonhomogeneous material. 



There is perhaps no observatory in the 

 world better located geographically for 

 carrying out a series of observations of 

 this kind than the Naval Observatory at 

 Washington. "While not an ideal climate for 

 astronomical work in general, the climate of 

 Washington is very good for work of thia 

 kind. The ground on which the observa- 

 tory is situated was chosen with special 

 reference to its suitability for the stable 

 support of instruments and also with re- 

 gard to freedom from unfavorable local 

 conditions. As regards its latitude, 38 de- 



