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 is any
change in the heavens, for one result of the enterprise has been
the discovery of thirteen of the new stars which now and then
blaze out in the heavens at points where none were before known.
Professor Pickering's work has been continually enlarged and