**3.4 Absorption Correction**

Finally, photometric apparent moduli must be corrected for galactic
absorption: *µ*_{0} = *µ* -
*A _{B}*; the correction was computed through the
following equation derived from a new analysis of the Mount Wilson
(Hubble's) counts
(de Vaucouleurs and
Malik 1969):

where

and

B_{1} | P | Q
| |

N.G.H. | -0.188 | -0.024 | -0.004 |

S.G.H. | -0.204 | -0.010 | +0.032. |

The value used here for the optical half-thickness of the Galaxy,
*A*_{1} =
0.2 mag, applies only to a sample selected by apparent brightness; it
agrees well with color-excess data
(Holmberg 1958;
de Vaucouleurs 1961a)
down to the lowest galactic latitudes.