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 would show to the eye.
This discovery was soon applied in various quarters. Sir David Gill,
with characteristic energy, photographed the stars of the southern sky
to the number of nearly half a million. As it was beyond his power to
measure off and compute the positions of the stars from his plates, the
latter were sent to Professor J. C. Kapteyn, of Holland, who undertook
the enormous labor of collecting them into a catalogue, the last volume
of which was published in 1899. One curious result of this enterprise
is that the work of listing the stars is more complete for the southern
hemisphere than for the northern.

Another great photographic work now in progress has to do with the
millions of stars which it is impossible to handle individually.
Fifteen years ago an association of observatories in both hemispheres
undertook to make a photographic chart of the sky on the largest scale.
Some portions of this work are now approaching completion, but in
others it is still in a backward state, owing to the failure of several
South American observatories to carry out their part of the programme.
When it is all done we shall have a picture of the sky, the study of
which may require the labor of a whole generation of astronomers.

Quite independently of this work, the Harvard University, under the
direction of Professor Pickering, keeps up the work of photographing
the sky on a surprising scale. On this plan we do not have to leave it
to posterity to learn whether there