undred lines with more precision than had then
been attained in the measurement of terrestrial spectra. This star
appeared to be virtually identical with the sun in physical
constitution, although it emits, according to the best available data,
about 140 times as much light, and is hence presumably 1,600 times more
voluminous. An equally close examination of the spectrum of Betelgeux
showed the predominance in it of the linear absorption of iron;[1430]
but its characteristic flutings do not extend to the photographic
region. Spectra of the second and third orders are for this reason not
easily distinguished on the sensitive plate.

A spectrographic investigation of all the brighter northern stars was
set on foot in 1886 at the observatory of Harvard College, under the
form of a memorial to Dr. H. Draper, whose promising work in that line
was brought to a close by his premature death in 1882. No individual
exertions could, however, have realized a tithe of what has been and is
being accomplished under Professor Pickering's able direction, with the
aid of the Draper and other instruments, supplemented by Mrs. Draper's
liberal provision of funds. A novel system was adopted, or, rather, an
old one--originally used by Fraunhofer--was revived.[1431] The use of a
slit was discarded as unnecessary for objects like the stars, devoid of
sensible dimensions, and giving hence a _naturally_ pure spectrum; and a
large prism, placed in front of the object-glass, analysed at once, with
slight loss of light, the rays of all the stars in the field. Their
spectra were taken, as it were, wholesale. As many as two hundred stars
down to the eighth magnitude were occasionally printed on a single plate
with a single exposure. No cylindrical lens was employed. The movement
of the stars themselves was turned to account for giving the desirable
width to their spectra. The star was allowed--by disconnecting or
suitably regulating the clock--to travel slowly across the line of its
own dispersed light, so broadening it gradually into a band. Excellent
results were secured in this way. About fifty lines appear in the
photographed spectrum of Aldebaran, and eight in that of Vega. On
January 26, 1886, with an exposure of thirty-four minutes, a
simultaneous impression was obtained of the spectra (among many others)
of close upon forty Pleiades. With few and doubtful exceptions, they all
proved to belong to the same type. An additional argument for the co