The earliest systems of classification
of ``nebulae'' by W. Herschel
and others have been described by H. D. Curtis in his article of the
``Handbuch der Astrophysik'' [A]
1. The spiral form of
some nebulae was first detected visually by Lord Rosse and his
assistants between 1845 and 1850 2 and the appellation
elliptical first used in a purely descriptive way was applied
to non-spiral tub presumably external stellar systems by S. Alexander
in 1852 3.
The great abundance of the spiral type
was brought to light by the
photographic surveys of the end of the XIX-th century. The spiral
structure of the Andromeda nebula was detected photographically in
1888 by I. Roberts. These surveys also revealed the great abundance of
smaller objects of the smooth, structureless elliptical type and the
very elongated objects described as ``spindles''. In 1918 Curtis
isolated a special type of spiral, the so-called ``'' type,
characterized by a diametral bar across the nucleus and a general
ring-like structure; he also identified the ``spindle'' nebulae with a
longitudinal dark lane as edgewise spirals with peripheral dark matter
An early alphabetical
classification of apparent shapes, introduced by M. Wolf 4,
has been extensively used at Heidelberg by
Reinmuth  and at Lund by
Lundmark , Holmberg,
Reiz, Danver and others 5. Its relation to the standard
classification has been given by Shapley and Ames
. For faint nebulae which
show little or no
structure, a descriptive classification, based on ``concentration'' and
``elongation'', introduced by Shapley 6 in 1929, has been
in use at Harvard for some years; it bears little relation to the
Rather similar systems of
morphological classification were
introduced, about 30 years ago, by Hubble
with three main types, viz. elliptical, spiral (normal and
barred) and irregular. This scheme, extensively used and later further
developed by Hubble, has been accepted as standard up to the present time.
1 The main references are listed at the end of the chapter
``General physical properties of external galaxies'', p. 311.
2 Earl of Rosse: Phil. Trans. Roy. Soc. Lond. 1850;
3 S. Alexander: Astronom. J. 2, 95.
4 M. Wolf: Verhöff. Königstuhl-Heidelberg
3, Nr. 5 (Plate V).
5 See Ann. Lund Obs. 6 (1937); 9 (1941);
6 H. Shapley: Harvard Bull. No. 849.