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INDEX

Age of Universe, 42, 43, 44, 62.

Bolometric luminosity, 33.

Cepheid variables, 9, 12, 14.
Clusters of nebulae, 10, 11, 36, 37, 38, 39, 40.
Copernican revolution, 2, 3.
Copernicus, 2, 3, 65.
Cosmological constant, 51, 62, 65.
Cosmological principles, 54.

Digges, Thomas, 3.
Distances of nebulae, 9 ff.
Distribution of nebulae, 15 ff.
   Distribution over the sky, 15 ff.
   Distribution in depth, 17 ff., 22, 49 ff., 56 ff., 64.
   Distribution in an expanding universe, 51 ff., 56 ff., 64.
   Distribution in a stationary universe, 47 ff., 59, 64.

Einstein, Albert, 53, 62.
Energy effect, 33 ff., 48, 49, 50, 57, 59.
Expanding universes of general relativity, 53 ff.
   Comparison of theory with observations, 56 ff.
   The permissible type of expanding universe, 61 ff.

Herschel, Sir William, 5.
Humason, Milton, 29.
Huygens, Christiaan, 3, 4.

Internebular material, 19, 20, 30, 50, 61, 62, 63.
Island Universes, theory of, 3, 4, 5.

Jeans, Sir James, 8.

Kant, Immanuel, 5.

Latitude effect, 16.
Local obscuration, 15 ff.
Luminosities of nebulae, 10, 11, 12, 13, 14.

Mayall, N. U., 46.
Milky Way, explanation of, 4.
Milne, E. A., 48, 53.

Nebulae,
   As Island Universes, 6.
   Characteristics of, 7, 8.
   Criteria of distances of, 9 ff.
   The average, 13 ff.
   Distribution of, 15 ff., 17 ff., 22, 49 ff., 56 ff., 64.
   Spectra of, 24, 25.
Newton, Sir Isaac, 3, 4.

Observable region of space, 1, 2, 7, 15, 18 ff., 39, 51, 64.
   Density of, 19, 62.

Possible worlds, 45 ff., 55, 56.

Recession factor, 32, 33, 34 ff., 51, 63.
Red-Shifts, 25 ff.
   Law of, 10, 20, 21, 25 ff.
   Interpretation of, 26 ff., 45.
   As velocity-shifts, 27 ff.
   As loss of energy in transit, 30 ff.
   Tests of alternative interpretations, 31 ff., 45.
   Effects on apparent luminosity, 32, 33, 45.
      Energy effect, 33 ff.
      Recession factor, 34 ff., 63.
   Formulation of law of red-shifts when interpreted
      As velocity shifts, 39 ff., 64.
      As loss of energy in transit, 36 ff., 64.
Reduction of surveys to a common epoch, 52, 53.
Relativistic cosmology, 41, 42, 53 ff.
Riemannian geometry, 55.

Slipher, V. M., 29.
Space absorption, 22, 50, 51, 62.
Spatial curvature, 55, 58 ff., 65.
Spectrum analysis, 23 ff.
   Types of spectra, 24.
   Nebular spectra, 24, 25.
Stars, early estimates of distances of, 3, 4.
Stellar system, isolation of, 4, 5.
Surveys of nebulae, 13, 46 ff., 52.

Universe of the Greeks, 2.
   Of general relativity, see Expanding universes.

Velocity-distance relation, 19, 42, 64.
Velocity-shifts, red-shifts as, 27 ff.

World Picture, 48, 49, 51.
Wright, Thomas, 4.

Zone of Avoidance for nebulae, 15, 17.


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