Among the nebulae of each separate type are found linear correlations
between total magnitudes and logarithms of diameters. These are
shown in Figures 2–5 for the beginning, middle, and end of the sequence
of types and also for the irregular nebulae. In Figures 2 and 3
adjacent types have been grouped in order to increase the material, and
in Figure 5 the Magellanic Clouds have been added to increase the range.