At Bonn he took an important part in preparing the Durchmusterung of the northern heavens.
A chart on an isographic projection, exhibiting all the stars contained in the Bonn Durchmusterung, was designed to show the laws according to which the stars down to the 9 - 10th magnitude are distributed over the northern heavens.
Seeliger, who investigated this ratio for the stars of the Bonn Durchmusterung and Southern Durchmusterung, came to the conclusion (as summarized by Simon Newcomb) that for these stars the ratio ranges from 3.85 to 3.28, the former value being found for regions near the Milky Way and the latter for regions near the galactic poles.
There is here evidence that even among stars of the Durchmusterung (9.5 magnitude), a limit of the universe has been reached, at least in the direction normal to the plane of the Milky Way.
Argelander, exact acquaintance was made with 90,000, a more general acquaintance with the 324,000 stars recorded in the Bonn Durchmusterung (1859-1862).
Photographic star-charting was begun by Sir David Gill in 1885, and the third and concluding volume of the Cape Photographic Durchmusterung appeared in 1900.
Kempf with a polarizing photometer; but by far the most comprehensive work of the kind is the Harvard Photometric Durchmusterung (1901-1903), embracing all stars to 7.5 magnitude, and extended to the southern pole by measurements executed at Arequipa.