TABLE VII ========+============+=========+=========+===== Type | ¯m¯_{T}$ | ¯log d¯ | C* | d† --------+------------+---------+---------+----- E0 | 11.40 | –0.204 | 10.38 | 1.2 1 | 11.43 | .177 | 10.54 | 1.3 2 | 11.52 | .088 | 11.08 | 1.6 3 | 11.99 | .133 | 11.33 | 1.8 4 | 11.95 | – .011 | 11.90 | 2.4 5 | 10.97 | + .090 | 11.42 | 1.9 6 | 10.93 | .220 | 12.03 | 2.5 7 | 11.02 | .360 | 12.82 | 3.7 | | | | Sa | 11.69 | .333 | 13.35 | 4.7 b | 11.55 | .471 | 13.90 | 6.0 c | 11.74 | .540 | 14.44 | 7.7 | | | | SBa | 11.66 | .267 | 13.00 | 4.0 b | 11.48 | .317 | 13.16 | 4.3 c | 11.87 | .509 | 14.41 | 7.6 | | | | Irr | 11.34 | +0.469 | 13.68 | 5.4 ------+- ----------+---------+---------+----- * C = $\overline{m}_{T} + 5 \overline{\log d}.$ † log d = 0.2 (C — m_{T}); m_{T} = 10.0. EFFECTS OF ORIENTATION The effect of the orientation is appreciable among the spirals in general. In order to illustrate this feature, they have been divided into three groups consisting of those whose images are round or nearly round, elliptical, and edge-on, or nearly so. The mean values of m_{T} + 5 log d were then computed and compared with the theoretical value, 13.0. The residuals are negative when the nebulae are too bright for their diameters and positive when they are too faint. The results are given in Table IX, where mean residuals are followed by the numbers of nebulae, in parentheses, which are represented by the means. The numbers of the barred spirals are too limited to inspire confidence in the results, but among the normal spirals there is conclusive evidence that the highly tilted and edge-on nebulae are fainter for a given diameter than those seen in the round. A study of the individual images indicates that the effect is due very largely to dark absorption clouds, which become more conspicuous when the nebulae are highly tilted. These clouds are generally, but not universally, peripheral features. An extensive investigation will be necessary before any residual effect due to absorption by luminous nebulosity can be established with certainty. Even should such exist, it clearly cannot be excessive.