F. Zwicky

The Coma Cluster of Galaxies

General remarks, The following study is a part of a long series of investigations which the author has carried out with the 18-inch and the 48-inch schmidt telescopes to analyze the geometrical distribution of the member galaxies in large regular and irregular clusters of galaxies. The strict definition of a galaxy as a physical object presents considerable difficulties. The whole of the astronomical literature has actually never produced such a definition. This neglect has resulted in some widely held erroneous views on the luminosity function of galaxies. The principal problem originates in the uncertainty regarding the objects which should be counted as separate entities. There is, for instance, the question of whether Messier 31 and its two companions should be counted as one system or as three. This uncertainty is greatly enhanced through the recent discovery by the author of the existence of intergalactic matter. Vast and often very irregular swarms of stars and other matter exist in the spaces between the conventional spiral, elliptical, and irregular galaxies. It is not at all clear how such swarms should be incorporated into any distribution function of galaxies. All of these questions must be cleared up in a comprehensive theory of the luminosity function of galaxies. In the present analysis we shall largely disregard the problems just mentioned. We shall simply count galaxies more or less naively, as has been done in the past. This procedure is quite sufficient to demonstrate that most of the counts of galaxies made with the large reflectors are subject to grave doubts. In particular the luminosity function of galaxies as derived from these counts is erroneous. For instance, the luminosity function given by Hubble1 has a sharp maximum at the absolute photographic magnitude Mp£=£ 14.2. The present writer has shown pre-

Luminous and dark formations of intergalactic matter

As astronomy pushed its limits from the solar system to the stars of the Milky Way and to the distant galaxies and clusters of galaxies, the following three problems suggested themselves automatically. Is there matter spread throughout interplanetary space? Is there matter in interstellar space? Are the enormous intergalactic spaces empty or not?

Clusters of Galaxies

The term nebulae means on the one hand clouds of gas and dust which are distributed among the stars. Within the Milky Way system, there are perhaps a few thousand of these galactic nebulae, their distribution exhibiting a decided preference for low galactic latitudes. The remaining objects, numbering hundreds of millions within the reach of the 200-inch telescope, are stellar systems distributed through extragalactic space. These systems, which, because of the absorption of light through the dust near the galactic plane, are mostly found in higher galactic latitudes, have been variously called island universes (Herschel), extragalactic nebulae or external galaxies. We shall refer to them simply as galaxies.

Objective transmission gratings for large Schmidt telescopes

Several lamellar gratings of 18-in. aperture, with 300 diffraction elements per inch, have been made for determining stellar spectra with wide angle telescopes. Central orders are missing at lambda4800, and weak at adjacent wavelengths. The two, equal first orders are about l(m) weaker than spectra by a prism or echelette grating. Dispersion is linear. The procedure of manufacture is adaptable to larger size. The wavelength at which the central order is missing can be controlled by varying the lamellae thickness. The lamellae are evaporated strips of quartz of 0.5-micro thickness, covering half the face of the support-a spectacle crown, plane parallel plate of ?-in. thickness. The lamellae were deposited by thermal evaporation.

PHYSICAL CHARACTERISTICS OF THE CANCER CLUSTER OF GALAXIES

The observed1 distribution of galaxies in the Cancer cluster suggests that this cluster has reached a fairly stationary state in the sense of statistical mechanics. It should consequently be possible to reduce the observed distribution of the member galaxies to that which is theoretically to be expected for atoms or molecules in a bounded isothermal gravitational gas sphere. R. Emden2 has quantitatively calculated this distribution for a sphere which contains particles of one mass only. The gas sphere which is composed of many elementary particles of different mass has so far not been amenable to exact