338 ANNUAL, KEPORT SMITHSONIAN INSTITUTION, 1910. 



Wright during the first two years and a half of the work of the D. O. 

 Mills expedition. The discovery of so many spectroscopic binaries 

 has greatly complicated the problem of determining the solar mo- 

 tion ; moreover, several other complexities have of late been added to 

 the analysis of the results. Eecent investigations of the proper mo- 

 tions of the stars made by Kapteyn, Eddington, Dyson, Schwarzs- 

 child, and others, have shown that our universe is probably complex 

 rather than homogeneous in respect to its structure, for there seem 

 to be at least two fairly well marked directions of motions among the 

 stars as a whole.^ Moreover, Monck and Kapteyn have pointed out 

 that a considerable majority of stars possessing marked proper mo- 

 tions belong to those sj^ectral types which show numerous lines of va- 

 rious elements, while the hydrogen and helium stars are relatively 

 fixed in space. In connection with these facts a further complexity is 

 brought in on the spectroscopic side through the unfortunate circum- 

 stance that it is not possible to derive accurate velocities for many of 

 the hydrogen and helium stars, because of the wide and hazy char- 

 acter of their spectral lines. A simple solution will then perhaps be 

 insufficient, on the assumption that all the velocities arrange them- 

 selves according to the probability curve ; it Avould seem that a satis- 

 factory conclusion can only be reached by a very careful combina- 

 tion of spectrographic results with due regard to all that the astron- 

 omy of position can give us with reference to " star-drift," proper 

 motions, and variation of proper motion with type of spectrum. 



Work on the determination of radial velocities has recently been 

 inaugurated at the Observatory of the Cape of Good Hope, so that 

 these two observatories, that at the Cape, and the D. O. Mills expedi- 

 tion, have to themselves this rich and still only partly explored field, 

 while in the Northern Hemisphere some 10 observatories are at work 

 on problems more or less allied to the determination of radial 

 velocities. 



In figure 1 are shown the locations of the principal observatories 

 of the world ; the cut is that given by Stroobant in Les Observatoires 

 Astronomiques et les Astronomes, Bruxelles, 1907, with the addition 

 of a few recently established stations. The map shows, better than 

 any description or tabulation, the overwhelming disproportion in the 

 number of astronomical foundations in the Northern and Southern 

 Hemispheres. 



Sufficient has been said to point out the great richness of the skies 

 of the Southern Hemisphere as a field for the working astronomer, 

 and note has been made of some of the lines of work in which there 

 are great untouched regions awaiting the explorer. Numerous other 



^ Recent investigations by Dr. Campbell, based upon his radial volocities for over 

 1^000 of the brighter stars, give but Jittle support to the two-drift hypothesis,— ^ 

 Author, May 9, 1911, 



