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 improved until about 150,000 photographic plates, showing
from time to time the places of countless millions of stars among their
fellows are now stored at the Harvard Observatory. Not less remarkable
than this wealth of material has been the development of skill in
working it up. Some idea of the work will be obtained by reflecting
that, thirty years ago, careful study of the heavens by astronomers
devoting their lives to the task had resulted in the discovery of some
two or three hundred stars, varying in their light. Now, at Harvard,
through keen eyes studying and comparing successive photographs not
only of isolated stars, but of clusters and agglomerations of stars in
the Milky Way and elsewhere, discoveries of such objects numbering
hundreds have been made, and the work is going on with ever-increasing
speed. Indeed, the number of variable stars now known is such that
their study as individual objects no longer suffices, and they must
hereafter be treated statistically with reference to their distribution
in space, and their relations to one another, as a census classifies
the entire population without taking any account of individuals.

The works just mentioned are concerned with the stars. But the heavenly
spaces contain nebulae as well as stars; and photography can now be
even more successful in picturing them than the stars. A few years ago
the late lamented Keeler, at the Lick Observatory, undertook to see
what could be done by pointing the Crossley reflecting telescope at the
sky and putting a sensitive photographic plate in the focus. He was
surprised to find that a great number of nebulae, the existence of
which had never before been suspected, were impressed on the plate. Up
to the present time the positions of about 8000 of these objects have
been listed. Keeler found that there were probably 200,000 nebulae in
the heavens capable of being photographed with the Crossley reflector.
But the work of taking these photographs is so great, and the number of
reflecting telescopes which can be applied to it so small, that no one
has ventured to seriously commence it. It is worthy of remark that only
a very small fraction of these objects which can be photogr