May 11, 1900.] 



SCIENCE. 



725 



The definitive results for the solar paral- 

 lax from the three planets separately were : 

 From Victoria : 8". 801 =t 0''.006 

 " Sappho: 8''. 798 ± 0^.011 

 " Iris: 8". 813 ±0". 009 



the combined result from the three, stated 

 in round numbers, is 8". 00. This value 

 has since been adopted, I believe, in all the 

 astronomical ephemerides. That it will 

 stand the test of time is however too much 

 to expect. The improvements now being 

 made in the means and the methods of re- 

 search will necessarily include the solar 

 parallax in their scope. But no change 

 that may thus be made in the accepted 

 value will diminish our admiration of the 

 skill, industry and ■ perseverance which our 

 medallist has spent upon his greatest work. 

 While the investigations which I have 

 mentioned, especially the last, are those 

 which the academy had in view in award- 

 ing its highest honor in the field of astron- 

 omy, there is a work of another class of the 

 first order of importance which cannot be 

 passed over in silence. I refer to the 

 ' Photographic Diirchmusterung ' of the 

 southern heavens, from 18° of south de- 

 clension to the pole. The third and com- 

 pleting volume of this work has just ap- 

 peared. It offers several features of general 

 interest. One is the curious fact that, with 

 its completion, we now have a better 

 knowledge of the stars of the southern 

 heavens, invisible in out latitudes, than we 

 have of the northern. It is an act of sim- 

 ple justice to one of our own countrymen 

 now pursuing his work in the Argentine 

 Republic, to say that this disparity in our 

 knowledge of the stars in the two hemi- 

 spheres is being markedly increased by the 

 survey of the southern heavens carried on 

 by Dr. Thome at the Argentine National 

 Observatory. The fact that Dr. Thome em- 

 ploys the visual method instead of pho- 

 tography adds to its value in the present 

 connection. 



This enterprise of Gill's is intimately 

 associated with the great international en- 

 terprise of making a photographic chart of 

 the heavens. In 1882 a great comet ap- 

 peared, and Gill engaged a Cape Photog- 

 rapher to take its picture. He was inter- 

 ested and surprised to find that along with 

 the comet were taken the surrounding stars 

 down to the 9 th magnitude. Evidently 

 here was a method of making star maps 

 which offered great advantages over the 

 laborious process of dotting down stars 

 from eye observation. He communicated 

 his suggestion to Admiral Mouchez, Direc- 

 tor of the Paris Observatory and the ques- 

 tion was taken up experimentally by the 

 Henrys. The result was the Paris Photo- 

 graphic Conference of 1887, which inaugu- 

 rated the enterprise now, we hope, approach- 

 ing its completion. 



An interesting circumstance may well 

 command our attention. The Cape Photo- 

 graphic Durchmusterung is the work of 

 two men, whose co- operation offers a re- 

 markable example of that disinterested de- 

 votion to the increase of knowledge which 

 is so conspicuous a mark of all modern 

 science. The mere taking of the photo- 

 graphs was not the whole work, it was not 

 even its main portion. The position of the 

 stars on the glass plates must be carefully 

 measured one by one, and every star-image 

 studied by itself, with the view to deter- 

 mine its magnitude. How was it possible 

 to devote the necessary attention to 350,000 

 separate objects? The one to do it was 

 found outside of all English connections in 

 the person of Professor J. C. Kapteyn, of 

 the University of Groningen, Holland. I 

 know not how many years of patient toil, 

 which would have made the fortune of a 

 business man, was spent by Kapteyn in this 

 work. What gives interest to it is that it 

 is an almost unique example in the history 

 of science of a man of the highest order of 

 general scientific ability in one country de- 



