August 16, 1907] 



SCIENCE 



209 



liam Huggins, in 1891, dealt so fully with 

 the chemistry of the stars that it seemed 

 fitting on the present occasion to consider 

 more especially the problem of their motion 

 and distribution in space, as it is in this 

 direction that the most striking advances 

 in our knowledge have recently been made. 

 It is true that since 1891 great advances 

 have also been made in our detailed knowl- 

 edge of the chemistry of the sun and stars. 

 The methods of astro-spectrography have 

 been greatly improved, the precision of the 

 determination of motion in the line of sight 

 greatly enhanced, and many discoveries 

 made of those close double stars, ordinarily 

 termed spectroscopic doubles, the study of 

 which seems destined to throw illustrative 

 light upon the probable history of the de- 

 velopment of systems from the original 

 nebular condition to that of more perma- 

 nent systems. 



But the limitations of available time 

 prevent me from entering more fully into 

 this tempting field, more especially as it 

 seems desirable, in the light of what has 

 been said, to indicate the directions in 

 which some of the astronomical work of 

 the future may be most properly systema- 

 tized. There are two aspects from which 

 this question may be viewed. The first is 

 the more or less immediate extension of 

 -knowledge or discovery ; the second the ful- 

 filment of our duty, as astronomers, to 

 future generations. These two aspects 

 should never be entirely separated. The 

 first, as it opens out new vistas of research 

 and improved methods of work, must often 

 serve as a guide to the objects of the 

 second. But the second is to the astron- 

 omer the supreme duty, viz., to secure for 

 future generations those data the value of 

 which grows by time. 



As the result of the Congress of As- 

 tronomers held at Paris in 1887 some six- 

 teen of the principal observatories in the 



world are engaged, as is well known, in the 

 laborious task, not only of photographing 

 the heavens, but of measuring these photo- 

 graphs and publishing the relative posi- 

 tions of the stars on the plates down to 

 the eleventh magnitude. A century hence 

 this great work will have to be repeated, 

 and then, if we of the present day have done 

 our duty thoroughly, our successors will 

 have the data for an infinitely more com- 

 plete and thorough discussion of the mo- 

 tions of the sidereal system than any that 

 can be attempted to-day. But there is still 

 needed the accurate meridian observation 

 of some eight or ten stars on each photo- 

 graphic plate, so as to permit the conver- 

 sion of the relative star-places on the plate 

 into absolute star-places in the heavens. It 

 is true that some of the astronomers have 

 already made these observations for the 

 reference stars of the zones which they 

 have undertaken. But this seems to be 

 hardly enough. In order to coordinate 

 these zones, as well as to give an accuracy 

 to the absolute positions of the reference 

 stars corresponding with that of the rela- 

 tive positions, it is desirable that this 

 should be done for all the reference stars 

 in the sky by several observatories. The 

 observations of well-distribvited stars by 

 Kustner at Bonn present an admirable in- 

 stance of the manner in which the work 

 should be done. Several observatories in 

 each hemisphere should devote themselves 

 to this work, employing the same or other 

 equally efficient means for the elimination 

 of sources of systematic error depending 

 on magnitude, etc., and it is of far more 

 importance that we should have, say, two 

 or three observations of each star at three 

 different observatories than two or three 

 times as many observations of each star 

 made at a single observatory. 



The southern can not boast of a richness 

 of instrumental and personal equipment 



