THE PROGRESS OF ASTRONOMY IN 1900. 147 
new pairs—a very notable addition to our knowledge of the 
stellar systems. Professor Aitken has discovered more than 
100 pairs, many of which are close and important. The year 
1900 is also distinguished by the publication of two unusu¬ 
ally important catalogues of double stars—(1) A General 
Catalogue of 1,270 Stars, discovered by S. W. Burnham be¬ 
tween 1870 and 1900, and (2) A Reference Catalogue of 
Double Stars in the Southern Hemisphere, by Mr. R. T. A. 
Innes, of the Royal Observatory, Cape of Good Hope. 
At Greenwich the spectroscopic binary Capella, which re¬ 
volves in a period of 104 days, has been observed visually 
by Lewis, Dyson, and others, and at last a connection between 
visual and spectroscopic pairs appears to be established. 
In the course of a general campaign on the motion of stars 
in the line of sight, Professor Campbell has investigated 285 
objects, of which 34 are spectroscopic binaries, all but three 
of which were discovered at the Lick Observatory by Camp¬ 
bell and Wright. The orbits of several have been worked 
out quite carefully, and in a general way they conform to 
the law among visual binaries, in showing high eccentricity, 
which Professor Campbell attributes to the secular effects of 
tidal friction. He also notes certain subsidiary undulations 
superposed upon the principal orbital motion, and explains 
thereby rotations and tidal motions in the fluids which cover 
the stars. He reaches the extraordinary result that one- 
ninth of all of the stars examined are spectroscopic binaries, 
some of the systems being triple, and two of the components 
being known already visually. 
£ Ursse Majoris and /c Pegasi are two of the well-known 
binary systems to which new components have been added. 
It is perhaps not too much to say that Professor Campbell’s 
researches open an entirely new field in stellar astronomy of 
immense extent, which cannot be too assiduously cultivated. 
It promises within a few years to very greatly enrich our 
knowledge of the sidereal universe, and will perhaps bring 
to light causes too delicate ever to be detected except by the 
spectroscopic method. 
21—Bull. Phil. Soe., Wash., Vol. 14. 
