$m_{T} = C - K \log d,$ (1)
where K is constant from type to type, but C varies progressively
throughout the sequence. The value of K cannot be accurately
determined from the scattered data for any particular type, but,
within the limits of uncertainty, it approximates the round number 5.0,
the value which is represented by the lines in Figures 2–5.
When K is known, the value of C can be computed from the mean magnitude
and the logarithm of the diameter for each type. This amounts to
reading from the curves the magnitudes corresponding to a diameter
of one minute of arc, but avoids the uncertainty of establishing the
curves where the data are limited.
TABLE IV
Irregular Nebulae
==========+===========+=========
N.G.C. | m_{T} | log d
----------+-----------+---------
2968 | 12.6 | +0.08
3034* | 9.0 | .85
3077 | 11.4 | .48
3729 | 11.8 | .17
4214* | 11.3 | .90
4449* | 9.5 | .65
4618 | 12.3 | +0.40
4656§ | 11.5 | +1.30
4753 | 11.4 | +0.43
5144 | 12.8 | – .30
5363 | 11.1 | +0.20
----------+-----------+---------
Mean | 11.34 | +0.469
----------+-----------+---------