s
of great service to the astronomer. It enabled him within the
comparatively short time of a single exposure to secure permanently
with great exactness the relative positions of hundreds or even of
thousands of stars, or the minute features of nebulae or other objects,
or the phenomena of a passing eclipse, a task which by means of the
eye and hand could only be accomplished, if done at all, after a very
great expenditure of time and labor. Photography put it in the power
of the astronomer to accomplish in the short span of his own life, and
so enter into their fruition, great works which otherwise must have
been passed on by him as a heritage of labor to succeeding
generations. The second great service which photography rendered was
not simply an aid to the powers the astronomer already possessed. On
the contrary, the plate, by recording light waves which were both too
small and too large to excite vision in the eye, brought him into a
new region of knowledge, such as the infra-red and the ultra-violet
parts of the spectrum, which must have remained forever unknown but
for artificial help.

A PHOTOGRAPHIC CHART.

The present year would be memorable in astronomical history for the
practical beginning of the photographic chart and catalogue of the
heavens which took their origin in an international conference which
met in Paris in 1887. The decisions of the conference in their final
form provided for the construction of a great chart with exposures
corresponding to forty minutes' exposure at Paris, which it was
expected would reach down to stars of about the fourteenth magnitude.
As each plate was to be limited to four square degrees, and as each
star, to avoid possible errors, was to appear on two plates, over
22,000 photographs would be required. A second set of plates for a
catalogue was to be taken, with a shorter exposure, which would give
stars to the eleventh magnitude only. The plans were to be pushed on
as actively a possible, though as far as might be practicable plates
for the chart were to be taken concurrently. Photographing the plates
for the catalogue was but the first step in this work, and only
supplied the data for the elaborate measurements which would have to
be made, which were, however, less laborious than would be required
for a similar catalogue without the aid of photography.

A DELICATE OPERATION.

The determination of the distances of the fixed stars from the small
apparent shift of