strong in the faint outlying parts of these nebulae. The
planetary nebula B.D.--12 degrees.1172 is seen in the ordinary
telescope to consist of a circular disc (probably a sphere or
spheroid) of light and a faint star in its center. When this
nebula is observed with a slitless spectrograph the hydrogen
and nebulium components are seen as circular discs, but the
hydrogen discs are larger than the nebulium discs. In other
words, the hydrogen forms an atmosphere about the central star
which extends out into space in all directions a great deal
farther than the nebulium discs extend. The Wolf-Rayet
star-planetary nebula D. M. + 30 degrees.3639 looks hazy in a
powerful telescope, and when examined in a spectroscope the
haziness is seen to be due to a sharply defined globe of
hydrogen 5 seconds of arc in diameter surrounding the star in
its center. Wolf and Burns have shown that in the Ring Nebula
in Lyra the 3726A and the hydrogen images are larger as to
outer diameter than the nebulium images, but that the latter
are the more condensed on the inner edge of the ring. Wright
has in the present year examined these and other nebulae with
special reference to the distribution of the principal
ingredients. He finds in general that the radiations at 4363A
and 4686A, of unknown or possibly helium origin, are most
closely compressed around the central nuclei of nebulae; that
the matter definitely known to be helium is more extended in
size; that the nebulium structure is still larger; and that the
hydrogen uniformly extends out farther than the nebulium; and
that the ultra violet radiation at 3726A seems to proceed from
the largest volume of all. The 37726A line, like the nebulium
line, is unknown in stellar spectra; it seems also to be
confined to true nebulosity. Neglecting the elements which have