mmon
origin of the stars forming this beautiful group was thus
provided.[1432]

The "Draper Catalogue" of stellar spectra was published in 1890.[1433]
It gives the results of a rapid analytical survey of the heavens north
of 25 deg. of southern declination, and includes 10,351 stars, down to
about the eighth magnitude. The telescope used was of eight inches
aperture and forty-five focus, its field of view--owing to the
"portrait-lens" or "doublet" form given to it--embracing with fair
definition no less than one hundred square degrees. An objective prism
eight inches square was attached, and exposures of a few minutes were
given to the most sensitive plates that could be procured. In this way
the sky was twice covered in duplicate, each star appearing, as a rule,
on four plates. The registration of their spectra was sought to be made
more distinctive than had previously been attempted, Secchi's first type
being divided into four, his second into five subdivisions; but the
differences regarded in them could be confidently established only for
stars above the sixth magnitude. The work supplies none the less valuable
materials for general inferences as to the distribution and relations of
the spectral types. The labour of its actual preparation was borne by a
staff of ladies under the direction of Mrs. Fleming. Materials for its
completion to the southern pole have been accumulated with the identical
instrument used at Cambridge, transferred for the purpose in 1889 to
Peru, and the forthcoming "Second Draper Catalogue" will comprise 30,000
stars in both hemispheres. As supplements to this great enterprise, two
important detailed discussions of stellar spectra were issued in 1897
and 1901 respectively.[1434] The first, by Miss A. C. Maury, dealt with
681 bright stars visible in the northern hemisphere; the second, by Miss
A. J. Cannon, with 1,122 southern stars. Both authors traced, with care
and ability, the minute gradations by which the long process of stellar
evolution appears to be accomplished.

The progress of the Draper Memorial researches was marked by discoveries
of an unexampled kind.

The principle upon which "motion in the line of sight" can be detected
and measured with the spectroscope has already been explained.[1435] It
depends, as our readers will remember, upon the removal of certain
lines, dark or bright (it matters not which), from their normal places
by almost infinitesimal amounts. The whole spectr