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3. DEVELOPMENT OF THE MODERN SYSTEM

3.1 Early Isolation of the Types

Reliable separation of galaxies into classes could successfully begin only after extensive photographic surveys were well underway, and the forms of galaxies discovered. This descriptive phase is not yet complete for the interacting galaxies (cf. Vorontsov-Velyaminov 1959; Zwicky 1959 and references therein), peculiar galaxies (Arp 1966), and perhaps even for the infinite detail of more regular systems (Vorontsov-Velyaminov, Krasnogorskaja, and Arkipova, in the four volumes of the Morphological Catalog of Galaxies 1962 - 1968). However, following the isolation of the S0 type by Hubble (cf. Spitzer and Baade 1951; Sandage 1961), of the dwarf ellipticals by Shapley (1938a, b) with the subsequent discovery of great numbers in the Local Group (cf. Harrington and Wilson 1950), and of dwarf spirals related to Magellanic Cloud-type Sm (cf. the Hubble Atlas, p. 40, for Dwf I and II in the NGC 1023 group), all the more common types of galaxies had been discovered by 1940.

If 1940 marks the end of the major survey for types, the beginning occurred in 1845 when spiral structure was first discovered visually in M51 by Lord Rosse with the 72- inch reflector at Burr Castle. According to Curtis (1933) spiral structure was subsequently identified by Rosse in perhaps 20 additional galaxies. The classical photographic work of Isaac Roberts from 1885 to 1904 confirmed the spiral types, and increased their number to about 40.

The photographic surveys of Keeler (1898-1900), Perrine (1901-1903), and Curtis (1909-1918; Lick Pub., 13, 1918) with the Lick Crossley reflector marks the beginning of research which led to the present classification. Mount Wilson survey's by Ritchey and by Pease (1917, 1920) with the 60-inch added to the material, as did the early systematic work of Knox-Shaw, Gregory, and Madwar with the Reynolds reflector at Helwan (Vols. 1 and 2 of Helwan Observatory Bulletins). Knox-Shaw (1915) and Reynolds (1920a) were among the first to call attention to amorphous galaxies with no trace of spiral arms (E systems). Curtis (1918) first isolated the barred spirals (called by him Phi type), and Lundmark (1926, 1927) emphasized the highly resolved Magellanic Cloud types, incorporating them as a separate group in his classification system.

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