the sky which we never see, because it is only visible from the
southern hemisphere, the corresponding work is far from being as
extensive. Sir David Gill, astronomer at the Cape of Good Hope,
and also the directors of other southern observatories, are
engaged in pushing it forward as rapidly as the limited facilities
at their disposal will allow.

Next in order comes the work of simply listing as many stars as
possible. Here the most exact positions are not required. It is
only necessary to lay down the position of each star with
sufficient exactness to distinguish it from all its neighbors.
About 400,000 stars were during the last half-century listed in
this way at the observatory of Bonn by Argelander, Schonfeld, and
their assistants. This work is now being carried through the
southern hemisphere on a large scale by Thome, Director of the
Cordoba Observatory, in the Argentine Republic. This was founded
thirty years ago by our Dr. B. A. Gould, who turned it over to Dr.
Thome in 1886. The latter has, up to the present time, fixed and
published the positions of nearly half a million stars. This work
of Thome extends to fainter stars than any other yet attempted, so
that, as it goes on, we have more stars listed in a region
invisible in middle northern latitudes than we have for that part
of the sky we can see. Up to the present time three quarto volumes
giving the positions and magnitudes of the stars have appeared.
Two or three volumes more, and, perhaps, ten or fifteen years,
will be required to complete the work.

About twenty years ago it was discovered that, by means of a
telescope especially adapted to this purpose, it was possible to
photograph many more stars than an instrument of the same size